← catalogue

A History of Science — Volume 4

by Henry Smith Williams · English · Gutenberg #1708 · 506,087 chars · public domain (US)

The Project Gutenberg eBook of A History of Science — Volume 4
    
This eBook is for the use of anyone anywhere in the United States and
most other parts of the world at no cost and with almost no restrictions
whatsoever. You may copy it, give it away or re-use it under the terms
of the Project Gutenberg License included with this eBook or online
at www.gutenberg.org. If you are not located in the United States,
you will have to check the laws of the country where you are located
before using this eBook.

Title: A History of Science — Volume 4

Author: Henry Smith Williams
        Edward Huntington Williams


        
Release date: April 1, 1999 [eBook #1708]
                Most recently updated: November 17, 2009

Language: English

Other information and formats: www.gutenberg.org/ebooks/1708

Credits: Produced by Charles Keller, and David Widger


*** START OF THE PROJECT GUTENBERG EBOOK A HISTORY OF SCIENCE — VOLUME 4 ***




Produced by Charles Keller





A HISTORY OF SCIENCE


By Henry Smith Williams, M.D., LL.D.

Assisted By Edward H. Williams, M.D.

In Five Volumes

Volume IV.


MODERN DEVELOPMENT OF THE CHEMICAL AND BIOLOGICAL SCIENCES




BOOK IV. MODERN DEVELOPMENT OF THE CHEMICAL AND BIOLOGICAL SCIENCES

AS regards chronology, the epoch covered in the present volume is
identical with that viewed in the preceding one. But now as regards
subject matter we pass on to those diverse phases of the physical world
which are the field of the chemist, and to those yet more intricate
processes which have to do with living organisms. So radical are the
changes here that we seem to be entering new worlds; and yet, here as
before, there are intimations of the new discoveries away back in the
Greek days. The solution of the problem of respiration will remind
us that Anaxagoras half guessed the secret; and in those diversified
studies which tell us of the Daltonian atom in its wonderful
transmutations, we shall be reminded again of the Clazomenian
philosopher and his successor Democritus.

Yet we should press the analogy much too far were we to intimate that
the Greek of the elder day or any thinker of a more recent period had
penetrated, even in the vaguest way, all of the mysteries that the
nineteenth century has revealed in the fields of chemistry and biology.
At the very most the insight of those great Greeks and of the wonderful
seventeenth-century philosophers who so often seemed on the verge of our
later discoveries did no more than vaguely anticipate their successors
of this later century. To gain an accurate, really specific knowledge of
the properties of elementary bodies was reserved for the chemists of a
recent epoch. The vague Greek questionings as to organic evolution were
world-wide from the precise inductions of a Darwin. If the mediaeval
Arabian endeavored to dull the knife of the surgeon with the use of
drugs, his results hardly merit to be termed even an anticipation
of modern anaesthesia. And when we speak of preventive medicine--of
bacteriology in all its phases--we have to do with a marvellous field of
which no previous generation of men had even the slightest inkling.

All in all, then, those that lie before us are perhaps the most
wonderful and the most fascinating of all the fields of science. As
the chapters of the preceding book carried us out into a macrocosm of
inconceivable magnitude, our present studies are to reveal a microcosm
of equally inconceivable smallness. As the studies of the physicist
attempted to reveal the very nature of matter and of energy, we have now
to seek the solution of the yet more inscrutable problems of life and of
mind.




I. THE PHLOGISTON THEORY IN CHEMISTRY

The development of the science of chemistry from the "science" of
alchemy is a striking example of the complete revolution in the attitude
of observers in the field of science. As has been pointed out in a
preceding chapter, the alchemist, having a preconceived idea of how
things should be, made all his experiments to prove his preconceived
theory; while the chemist reverses this attitude of mind and bases his
conceptions on the results of his laboratory experiments. In short,
chemistry is what alchemy never could be, an inductive science. But
this transition from one point of view to an exactly opposite one was
necessarily a very slow process. Ideas that have held undisputed sway
over the minds of succeeding generations for hundreds of years cannot
be overthrown in a moment, unless the agent of such an overthrow be so
obvious that it cannot be challenged. The rudimentary chemistry that
overthrew alchemy had nothing so obvious and palpable.

The great first step was the substitution of the one principle,
phlogiston, for the three principles, salt, sulphur, and mercury. We
have seen how the experiment of burning or calcining such a metal
as lead "destroyed" the lead as such, leaving an entirely different
substance in its place, and how the original metal could be restored by
the addition of wheat to the calcined product. To the alchemist this was
"mortification" and "revivification" of the metal. For, as pointed
out by Paracelsus, "anything that could be killed by man could also be
revivified by him, although this was not possible to the things killed
by God." The burning of such substances as wood, wax, oil, etc., was
also looked upon as the same "killing" process, and the fact that the
alchemist was unable to revivify them was regarded as simply the lack of
skill on his part, and in no wise affecting the theory itself.

But the iconoclastic spirit, if not the acceptance of all the teachings,
of the great Paracelsus had been gradually taking root among the better
class of alchemists, and about the middle of the seventeenth century
Robert Boyle (1626-1691) called attention to the possibility of making
a wrong deduction from the phenomenon of the calcination of the metals,
because of a very important factor, the action of the air, which was
generally overlooked. And he urged his colleagues of the laboratories to
give greater heed to certain other phenomena that might pass unnoticed
in the ordinary calcinating process. In his work, The Sceptical Chemist,
he showed the reasons for doubting the threefold constitution of matter;
and in his General History of the Air advanced some novel and carefully
studied theories as to the composition of the atmosphere. This was an
important step, and although Boyle is not directly responsible for the
phlogiston theory, it is probable that his experiments on the atmosphere
influenced considerably the real founders, Becker and Stahl.

Boyle gave very definitely his idea of how he thought air might be
composed. "I conjecture that the atmospherical air consists of three
different kinds of corpuscles," he says; "the first, those numberless
particles which, in the form of vapors or dry exhalations, ascend
from the earth, water, minerals, vegetables, animals, etc.; in a word,
whatever substances are elevated by the celestial or subterraneal heat,
and thence diffused into the atmosphere. The second may be yet more
subtle, and consist of those exceedingly minute atoms, the magnetical
effluvia of the earth, with other innumerable particles sent out from
the bodies of the celestial luminaries, and causing, by their influence,
the idea of light in us. The third sort is its characteristic and
essential property, I mean permanently elastic parts. Various hypotheses
may be framed relating to the structure of these later particles of the
air. They might be resembled to the springs of watches, coiled up and
endeavoring to restore themselves; to wool, which, being compressed,
has an elastic force; to slender wires of different substances,
consistencies, lengths, and thickness; in greater curls or less,
near to, or remote from each other, etc., yet all continuing springy,
expansible, and compressible. Lastly, they may also be compared to the
thin shavings of different kinds of wood, various in their lengths,
breadth, and thickness. And this, perhaps, will seem the most eligible
hypothesis, because it, in some measure, illustrates the production
of the elastic particles we are considering. For no art or curious
instruments are required to make these shavings whose curls are in no
wise uniform, but seemingly casual; and what is more remarkable, bodies
that before seemed unelastic, as beams and blocks, will afford them."(1)

Although this explanation of the composition of the air is most crude,
it had the effect of directing attention to the fact that the
atmosphere is not "mere nothingness," but a "something" with a
definite composition, and this served as a good foundation for future
investigations. To be sure, Boyle was neither the first nor the only
chemist who had suspected that the air was a mixture of gases, and not
a simple one, and that only certain of these gases take part in the
process of calcination. Jean Rey, a French physician, and John Mayow, an
Englishman, had preformed experiments which showed conclusively that the
air was not a simple substance; but Boyle's work was better known, and
in its effect probably more important. But with all Boyle's explanations
of the composition of air, he still believed that there was an
inexplicable something, a "vital substance," which he was unable to
fathom, and which later became the basis of Stahl's phlogiston theory.
Commenting on this mysterious substance, Boyle says: "The difficulty
we find in keeping flame and fire alive, though but for a little time,
without air, renders it suspicious that there be dispersed through the
rest of the atmosphere some odd substance, either of a solar, astral, or
other foreign nature; on account of which the air is so necessary to the
substance of flame!" It was this idea that attracted the attention
of George Ernst Stahl (1660-1734), a professor of medicine in the
University of Halle, who later founded his new theory upon it. Stahl's
theory was a development of an earlier chemist, Johann Joachim Becker
(1635-1682), in whose footsteps he followed and whose experiments he
carried further.

In many experiments Stahl had been struck with the fact that certain
substances, while differing widely, from one another in many respects,
were alike in combustibility. From this he argued that all combustible
substances must contain a common principle, and this principle he named
phlogiston. This phlogiston he believed to be intimately associated in
combination with other substances in nature, and in that condition not
perceivable by the senses; but it was supposed to escape as a substance
burned, and become apparent to the senses as fire or flame. In other
words, phlogiston was something imprisoned in a combustible structure
(itself forming part of the structure), and only liberated when this
structure was destroyed. Fire, or flame, was FREE phlogiston, while the
imprisoned phlogiston was called COMBINED PHLOGISTON, or combined fire.
The peculiar quality of this strange substance was that it disliked
freedom and was always striving to conceal itself in some combustible
substance. Boyle's tentative suggestion that heat was simply motion was
apparently not accepted by Stahl, or perhaps it was unknown to him.

According to the phlogistic theory, the part remaining after a substance
was burned was simply the original substance deprived of phlogiston. To
restore the original combustible substance, it was necessary to heat the
residue of the combustion with something that burned easily, so that the
freed phlogiston might again combine with the ashes. This was explained
by the supposition that the more combustible a substance was the more
phlogiston it contained, and since free phlogiston sought always to
combine with some suitable substance, it was only necessary to mix the
phlogisticating agents, such as charcoal, phosphorus, oils, fats, etc.,
with the ashes of the original substance, and heat the mixture, the
phlogiston thus freed uniting at once with the ashes. This theory fitted
very nicely as applied to the calcined lead revivified by the grains of
wheat, although with some other products of calcination it did not seem
to apply at all.

It will be seen from this that the phlogistic theory was a step towards
chemistry and away from alchemy. It led away from the idea of a "spirit"
in metals that could not be seen, felt, or appreciated by any of the
senses, and substituted for it a principle which, although a falsely
conceived one, was still much more tangible than the "spirit," since it
could be seen and felt as free phlogiston and weighed and measured as
combined phlogiston. The definiteness of the statement that a metal,
for example, was composed of phlogiston and an element was much less
enigmatic, even if wrong, than the statement of the alchemist that
"metals are produced by the spiritual action of the three principles,
salt, mercury, sulphur"--particularly when it is explained that salt,
mercury, and sulphur were really not what their names implied, and that
there was no universally accepted belief as to what they really were.

The metals, which are now regarded as elementary bodies, were considered
compounds by the phlogistians, and they believed that the calcining of
a metal was a process of simplification. They noted, however, that the
remains of calcination weighed more than the original product, and the
natural inference from this would be that the metal must have taken in
some substance rather than have given off anything. But the phlogistians
had not learned the all-important significance of weights, and their
explanation of variation in weight was either that such gain or loss
was an unimportant "accident" at best, or that phlogiston, being light,
tended to lighten any substance containing it, so that driving it out of
the metal by calcination naturally left the residue heavier.

At first the phlogiston theory seemed to explain in an indisputable way
all the known chemical phenomena. Gradually, however, as experiments
multiplied, it became evident that the plain theory as stated by Stahl
and his followers failed to explain satisfactorily certain laboratory
reactions. To meet these new conditions, certain modifications were
introduced from time to time, giving the theory a flexibility that
would allow it to cover all cases. But as the number of inexplicable
experiments continued to increase, and new modifications to the theory
became necessary, it was found that some of these modifications were
directly contradictory to others, and thus the simple theory became
too cumbersome from the number of its modifications. Its supporters
disagreed among themselves, first as to the explanation of certain
phenomena that did not seem to accord with the phlogistic theory, and
a little later as to the theory itself. But as yet there was no
satisfactory substitute for this theory, which, even if unsatisfactory,
seemed better than anything that had gone before or could be suggested.

But the good effects of the era of experimental research, to which the
theory of Stahl had given such an impetus, were showing in the attitude
of the experimenters. The works of some of the older writers, such
as Boyle and Hooke, were again sought out in their dusty corners and
consulted, and their surmises as to the possible mixture of various
gases in the air were more carefully considered. Still the phlogiston
theory was firmly grounded in the minds of the philosophers, who can
hardly be censured for adhering to it, at least until some satisfactory
substitute was offered. The foundation for such a theory was finally
laid, as we shall see presently, by the work of Black, Priestley,
Cavendish, and Lavoisier, in the eighteenth century, but the phlogiston
theory cannot be said to have finally succumbed until the opening years
of the nineteenth century.




II. THE BEGINNINGS OF MODERN CHEMISTRY

THE "PNEUMATIC" CHEMISTS

Modern chemistry may be said to have its beginning with the work of
Stephen Hales (1677-1761), who early in the eighteenth century began his
important study of the elasticity of air. Departing from the point of
view of most of the scientists of the time, he considered air to be "a
fine elastic fluid, with particles of very different nature floating in
it"; and he showed that these "particles" could be separated. He pointed
out, also, that various gases, or "airs," as he called them, were
contained in many solid substances. The importance of his work, however,
lies in the fact that his general studies were along lines leading away
from the accepted doctrines of the time, and that they gave the impetus
to the investigation of the properties of gases by such chemists as
Black, Priestley, Cavendish, and Lavoisier, whose specific discoveries
are the foundation-stones of modern chemistry.


JOSEPH BLACK

The careful studies of Hales were continued by his younger confrere, Dr.
Joseph Black (1728-1799), whose experiments in the weights of gases and
other chemicals were first steps in quantitative chemistry. But even
more important than his discoveries of chemical properties in general
was his discovery of the properties of carbonic-acid gas.

Black had been educated for the medical profession in the University of
Glasgow, being a friend and pupil of the famous Dr. William Cullen. But
his liking was for the chemical laboratory rather than for the practice
of medicine. Within three years after completing his medical course,
and when only twenty-three years of age, he made the discovery of the
properties of carbonic acid, which he called by the name of "fixed air."
After discovering this gas, Black made a long series of experiments,
by which he was able to show how widely it was distributed throughout
nature. Thus, in 1757, he discovered that the bubbles given off in
the process of brewing, where there was vegetable fermentation, were
composed of it. To prove this, he collected the contents of these
bubbles in a bottle containing lime-water. When this bottle was
shaken violently, so that the lime-water and the carbonic acid became
thoroughly mixed, an insoluble white powder was precipitated from the
solution, the carbonic acid having combined chemically with the lime
to form the insoluble calcium carbonate, or chalk. This experiment
suggested another. Fixing a piece of burning charcoal in the end of a
bellows, he arranged a tube so that the gas coming from the charcoal
would pass through the lime-water, and, as in the case of the bubbles
from the brewer's vat, he found that the white precipitate was thrown
down; in short, that carbonic acid was given off in combustion. Shortly
after, Black discovered that by blowing through a glass tube inserted
into lime-water, chalk was precipitated, thus proving that carbonic acid
was being constantly thrown off in respiration.

The effect of Black's discoveries was revolutionary, and the attitude
of mind of the chemists towards gases, or "airs," was changed from that
time forward. Most of the chemists, however, attempted to harmonize the
new facts with the older theories--to explain all the phenomena on the
basis of the phlogiston theory, which was still dominant. But while many
of Black's discoveries could not be made to harmonize with that
theory, they did not directly overthrow it. It required the additional
discoveries of some of Black's fellow-scientists to complete its
downfall, as we shall see.


HENRY CAVENDISH

This work of Black's was followed by the equally important work of
his former pupil, Henry Cavendish (1731-1810), whose discovery of the
composition of many substances, notably of nitric acid and of water,
was of great importance, adding another link to the important chain of
evidence against the phlogiston theory. Cavendish is one of the most
eccentric figures in the history of science, being widely known in his
own time for his immense wealth and brilliant intellect, and also for
his peculiarities and his morbid sensibility, which made him dread
society, and probably did much in determining his career. Fortunately
for him, and incidentally for the cause of science, he was able to
pursue laboratory investigations without being obliged to mingle with
his dreaded fellow-mortals, his every want being provided for by the
immense fortune inherited from his father and an uncle.

When a young man, as a pupil of Dr. Black, he had become imbued with the
enthusiasm of his teacher, continuing Black's investigations as to the
properties of carbonic-acid gas when free and in combination. One of his
first investigations was reported in 1766, when he communicated to
the Royal Society his experiments for ascertaining the properties of
carbonic-acid and hydrogen gas, in which he first showed the possibility
of weighing permanently elastic fluids, although Torricelli had before
this shown the relative weights of a column of air and a column of
mercury. Other important experiments were continued by Cavendish, and
in 1784 he announced his discovery of the composition of water, thus
robbing it of its time-honored position as an "element." But his
claim to priority in this discovery was at once disputed by his
fellow-countryman James Watt and by the Frenchman Lavoisier. Lavoisier's
claim was soon disallowed even by his own countrymen, but for many
years a bitter controversy was carried on by the partisans of Watt and
Cavendish. The two principals, however, seem never to have entered
into this controversy with anything like the same ardor as some of their
successors, as they remained on the best of terms.(1) It is certain, at
any rate, that Cavendish announced his discovery officially before Watt
claimed that the announcement had been previously made by him, "and,
whether right or wrong, the honor of scientific discoveries seems to be
accorded naturally to the man who first publishes a demonstration of his
discovery." Englishmen very generally admit the justness of Cavendish's
claim, although the French scientist Arago, after reviewing the evidence
carefully in 1833, decided in favor of Watt.

It appears that something like a year before Cavendish made known his
complete demonstration of the composition of water, Watt communicated
to the Royal Society a suggestion that water was composed of
"dephlogisticated air (oxygen) and phlogiston (hydrogen) deprived of
part of its latent heat." Cavendish knew of the suggestion, but in his
experiments refuted the idea that the hydrogen lost any of its latent
heat. Furthermore, Watt merely suggested the possible composition
without proving it, although his idea was practically correct, if we can
rightly interpret the vagaries of the nomenclature then in use. But
had Watt taken the steps to demonstrate his theory, the great "Water
Controversy" would have been avoided. Cavendish's report of his
discovery to the Royal Society covers something like forty pages of
printed matter. In this he shows how, by passing an electric spark
through a closed jar containing a mixture of hydrogen gas and oxygen,
water is invariably formed, apparently by the union of the two gases.
The experiment was first tried with hydrogen and common air, the oxygen
of the air uniting with the hydrogen to form water, leaving the nitrogen
of the air still to be accounted for. With pure oxygen and hydrogen,
however, Cavendish found that pure water was formed, leaving slight
traces of any other, substance which might not be interpreted as being
Chemical impurities. There was only one possible explanation of this
phenomenon--that hydrogen and oxygen, when combined, form water.

"By experiments with the globe it appeared," wrote Cavendish, "that when
inflammable and common air are exploded in a proper proportion, almost
all the inflammable air, and near one-fifth the common air, lose their
elasticity and are condensed into dew. And by this experiment it appears
that this dew is plain water, and consequently that almost all the
inflammable air is turned into pure water.

"In order to examine the nature of the matter condensed on firing a
mixture of dephlogisticated and inflammable air, I took a glass
globe, holding 8800 grain measures, furnished with a brass cock and an
apparatus for firing by electricity. This globe was well exhausted by
an air-pump, and then filled with a mixture of inflammable and
dephlogisticated air by shutting the cock, fastening the bent glass tube
into its mouth, and letting up the end of it into a glass jar inverted
into water and containing a mixture of 19,500 grain measures of
dephlogisticated air, and 37,000 of inflammable air; so that, upon
opening the cock, some of this mixed air rushed through the bent tube
and filled the globe. The cock was then shut and the included air fired
by electricity, by means of which almost all of it lost its elasticity
(was condensed into water vapors). The cock was then again opened so as
to let in more of the same air to supply the place of that destroyed by
the explosion, which was again fired, and the operation continued till
almost the whole of the mixture was let into the globe and exploded.
By this means, though the globe held not more than a sixth part of the
mixture, almost the whole of it was exploded therein without any fresh
exhaustion of the globe."

At first this condensed matter was "acid to the taste and contained
two grains of nitre," but Cavendish, suspecting that this was due to
impurities, tried another experiment that proved conclusively that his
opinions were correct. "I therefore made another experiment," he says,
"with some more of the same air from plants in which the proportion of
inflammable air was greater, so that the burnt air was almost completely
phlogisticated, its standard being one-tenth. The condensed liquor was
then not at all acid, but seemed pure water."

From these experiments he concludes "that when a mixture of inflammable
and dephlogisticated air is exploded, in such proportions that the burnt
air is not much phlogisticated, the condensed liquor contains a little
acid which is always of the nitrous kind, whatever substance the
dephlogisticated air is procured from; but if the proportion be such
that the burnt air is almost entirely phlogisticated, the condensed
liquor is not at all acid, but seems pure water, without any addition
whatever."(2)

These same experiments, which were undertaken to discover the
composition of water, led him to discover also the composition of nitric
acid. He had observed that, in the combustion of hydrogen gas with
common air, the water was slightly tinged with acid, but that this
was not the case when pure oxygen gas was used. Acting upon this
observation, he devised an experiment to determine the nature of this
acid. He constructed an apparatus whereby an electric spark was passed
through a vessel containing common air. After this process had been
carried on for several weeks a small amount of liquid was formed. This
liquid combined with a solution of potash to form common nitre, which
"detonated with charcoal, sparkled when paper impregnated with it was
burned, and gave out nitrous fumes when sulphuric acid was poured on
it." In other words, the liquid was shown to be nitric acid. Now, since
nothing but pure air had been used in the initial experiment, and since
air is composed of nitrogen and oxygen, there seemed no room to doubt
that nitric acid is a combination of nitrogen and oxygen.

This discovery of the nature of nitric acid seems to have been about the
last work of importance that Cavendish did in the field of chemistry,
although almost to the hour of his death he was constantly occupied with
scientific observations. Even in the last moments of his life this habit
asserted itself, according to Lord Brougham. "He died on March 10, 1810,
after a short illness, probably the first, as well as the last, which he
ever suffered. His habit of curious observation continued to the end.
He was desirous of marking the progress of the disease and the gradual
extinction of the vital powers. With these ends in view, that he might
not be disturbed, he desired to be left alone. His servant, returning
sooner than he had wished, was ordered again to leave the chamber of
death, and when he came back a second time he found his master had
expired."(3)


JOSEPH PRIESTLEY

While the opulent but diffident Cavendish was making his important
discoveries, another Englishman, a poor country preacher named Joseph
Priestley (1733-1804) was not only rivalling him, but, if anything,
outstripping him in the pursuit of chemical discoveries. In 1761 this
young minister was given a position as tutor in a nonconformist academy
at Warrington, and here, for six years, he was able to pursue his
studies in chemistry and electricity. In 1766, while on a visit to
London, he met Benjamin Franklin, at whose suggestion he published his
History of Electricity. From this time on he made steady progress in
scientific investigations, keeping up his ecclesiastical duties at the
same time. In 1780 he removed to Birmingham, having there for associates
such scientists as James Watt, Boulton, and Erasmus Darwin.

Eleven years later, on the anniversary of the fall of the Bastile in
Paris, a fanatical mob, knowing Priestley's sympathies with the
French revolutionists, attacked his house and chapel, burning both and
destroying a great number of valuable papers and scientific instruments.
Priestley and his family escaped violence by flight, but his most
cherished possessions were destroyed; and three years later he quitted
England forever, removing to the United States, whose struggle for
liberty he had championed. The last ten years of his life were spent
at Northumberland, Pennsylvania, where he continued his scientific
researches.

Early in his scientific career Priestley began investigations upon the
"fixed air" of Dr. Black, and, oddly enough, he was stimulated to this
by the same thing that had influenced Black--that is, his residence in
the immediate neighborhood of a brewery. It was during the course of a
series of experiments on this and other gases that he made his greatest
discovery, that of oxygen, or "dephlogisticated air," as he called
it. The story of this important discovery is probably best told in
Priestley's own words:

"There are, I believe, very few maxims in philosophy that have laid
firmer hold upon the mind than that air, meaning atmospheric air, is a
simple elementary substance, indestructible and unalterable, at least as
much so as water is supposed to be. In the course of my inquiries I
was, however, soon satisfied that atmospheric air is not an unalterable
thing; for that, according to my first hypothesis, the phlogiston with
which it becomes loaded from bodies burning in it, and the animals
breathing it, and various other chemical processes, so far alters
and depraves it as to render it altogether unfit for inflammation,
respiration, and other purposes to which it is subservient; and I had
discovered that agitation in the water, the process of vegetation, and
probably other natural processes, restore it to its original purity....

"Having procured a lens of twelve inches diameter and twenty inches
local distance, I proceeded with the greatest alacrity, by the help of
it, to discover what kind of air a great variety of substances would
yield, putting them into the vessel, which I filled with quicksilver,
and kept inverted in a basin of the same .... With this apparatus, after
a variety of experiments.... on the 1st of August, 1774, I endeavored
to extract air from mercurius calcinatus per se; and I presently found
that, by means of this lens, air was expelled from it very readily.
Having got about three or four times as much as the bulk of my
materials, I admitted water to it, and found that it was not imbibed
by it. But what surprised me more than I can express was that a candle
burned in this air with a remarkably vigorous flame, very much like that
enlarged flame with which a candle burns in nitrous oxide, exposed to
iron or liver of sulphur; but as I had got nothing like this remarkable
appearance from any kind of air besides this particular modification of
vitrous air, and I knew no vitrous acid was used in the preparation of
mercurius calcinatus, I was utterly at a loss to account for it."(4)


The "new air" was, of course, oxygen. Priestley at once proceeded to
examine it by a long series of careful experiments, in which, as will
be seen, he discovered most of the remarkable qualities of this gas.
Continuing his description of these experiments, he says:

"The flame of the candle, besides being larger, burned with more
splendor and heat than in that species of nitrous air; and a piece of
red-hot wood sparkled in it, exactly like paper dipped in a solution of
nitre, and it consumed very fast; an experiment that I had never thought
of trying with dephlogisticated nitrous air.

"... I had so little suspicion of the air from the mercurius calcinatus,
etc., being wholesome, that I had not even thought of applying it to
the test of nitrous air; but thinking (as my reader must imagine I
frequently must have done) on the candle burning in it after long
agitation in water, it occurred to me at last to make the experiment;
and, putting one measure of nitrous air to two measures of this air, I
found not only that it was diminished, but that it was diminished quite
as much as common air, and that the redness of the mixture was likewise
equal to a similar mixture of nitrous and common air.... The next day I
was more surprised than ever I had been before with finding that, after
the above-mentioned mixture of nitrous air and the air from mercurius
calcinatus had stood all night,... a candle burned in it, even better
than in common air."

A little later Priestley discovered that "dephlogisticated air... is a
principal element in the composition of acids, and may be extracted by
means of heat from many substances which contain them.... It is likewise
produced by the action of light upon green vegetables; and this seems to
be the chief means employed to preserve the purity of the atmosphere."

This recognition of the important part played by oxygen in the
atmosphere led Priestley to make some experiments upon mice and insects,
and finally upon himself, by inhalations of the pure gas. "The feeling
in my lungs," he said, "was not sensibly different from that of common
air, but I fancied that my breathing felt peculiarly light and easy for
some time afterwards. Who can tell but that in time this pure air may
become a fashionable article in luxury?... Perhaps we may from these
experiments see that though pure dephlogisticated air might be useful as
a medicine, it might not be so proper for us in the usual healthy state
of the body."

This suggestion as to the possible usefulness of oxygen as a medicine
was prophetic. A century later the use of oxygen had become a matter of
routine practice with many physicians. Even in Priestley's own time such
men as Dr. John Hunter expressed their belief in its efficacy in certain
conditions, as we shall see, but its value in medicine was not fully
appreciated until several generations later.

Several years after discovering oxygen Priestley thus summarized its
properties: "It is this ingredient in the atmospheric air that enables
it to support combustion and animal life. By means of it most intense
heat may be produced, and in the purest of it animals will live nearly
five times as long as in an equal quantity of atmospheric air. In
respiration, part of this air, passing the membranes of the lungs,
unites with the blood and imparts to it its florid color, while the
remainder, uniting with phlogiston exhaled from venous blood, forms
mixed air. It is dephlogisticated air combined with water that enables
fishes to live in it."(5)


KARL WILHELM SCHEELE

The discovery of oxygen was the last but most important blow to the
tottering phlogiston theory, though Priestley himself would not admit
it. But before considering the final steps in the overthrow of Stahl's
famous theory and the establishment of modern chemistry, we must review
the work of another great chemist, Karl Wilhelm Scheele (1742-1786), of
Sweden, who discovered oxygen quite independently, although later than
Priestley. In the matter of brilliant discoveries in a brief space of
time Scheele probably eclipsed all his great contemporaries. He had a
veritable genius for interpreting chemical reactions and discovering
new substances, in this respect rivalling Priestley himself. Unlike
Priestley, however, he planned all his experiments along the lines of
definite theories from the beginning, the results obtained being the
logical outcome of a predetermined plan.

Scheele was the son of a merchant of Stralsund, Pomerania, which then
belonged to Sweden. As a boy in school he showed so little aptitude for
the study of languages that he was apprenticed to an apothecary at the
age of fourteen. In this work he became at once greatly interested, and,
when not attending to his duties in the dispensary, he was busy day and
night making experiments or studying books on chemistry. In 1775, still
employed as an apothecary, he moved to Stockholm, and soon after he sent
to Bergman, the leading chemist of Sweden, his first discovery--that of
tartaric acid, which he had isolated from cream of tartar. This was the
beginning of his career of discovery, and from that time on until his
death he sent forth accounts of new discoveries almost uninterruptedly.
Meanwhile he was performing the duties of an ordinary apothecary, and
struggling against poverty. His treatise upon Air and Fire appeared
in 1777. In this remarkable book he tells of his discovery of
oxygen--"empyreal" or "fire-air," as he calls it--which he seems to
have made independently and without ever having heard of the previous
discovery by Priestley. In this book, also, he shows that air is
composed chiefly of oxygen and nitrogen gas.

Early in his experimental career Scheele undertook the solution of
the composition of black oxide of manganese, a substance that had long
puzzled the chemists. He not only succeeded in this, but incidentally in
the course of this series of experiments he discovered oxygen, baryta,
and chlorine, the last of far greater importance, at least commercially,
than the real object of his search. In speaking of the experiment in
which the discovery was made he says:

"When marine (hydrochloric) acid stood over manganese in the cold it
acquired a dark reddish-brown color. As manganese does not give any
colorless solution without uniting with phlogiston (probably meaning
hydrogen), it follows that marine acid can dissolve it without this
principle. But such a solution has a blue or red color. The color is
here more brown than red, the reason being that the very finest portions
of the manganese, which do not sink so easily, swim in the red solution;
for without these fine particles the solution is red, and red mixed with
black is brown. The manganese has here attached itself so loosely to
acidum salis that the water can precipitate it, and this precipitate
behaves like ordinary manganese. When, now, the mixture of manganese and
spiritus salis was set to digest, there arose an effervescence and smell
of aqua regis."(6)

The "effervescence" he refers to was chlorine, which he proceeded to
confine in a suitable vessel and examine more fully. He described it as
having a "quite characteristically suffocating smell," which was very
offensive. He very soon noted the decolorizing or bleaching effects of
this now product, finding that it decolorized flowers, vegetables, and
many other substances.

Commercially this discovery of chlorine was of enormous importance and
the practical application of this new chemical in bleaching cloth soon
supplanted the old process of crofting--that is, bleaching by spreading
the cloth upon the grass. But although Scheele first pointed out the
bleaching quality of his newly discovered gas, it was the French savant,
Berthollet, who, acting upon Scheele's discovery that the new gas would
decolorize vegetables and flowers, was led to suspect that this property
might be turned to account in destroying the color of cloth. In 1785 he
read a paper before the Academy of Sciences of Paris, in which he showed
that bleaching by chlorine was entirely satisfactory, the color but
not the substance of the cloth being affected. He had experimented
previously and found that the chlorine gas was soluble in water and
could thus be made practically available for bleaching purposes. In 1786
James Watt examined specimens of the bleached cloth made by Berthollet,
and upon his return to England first instituted the process of practical
bleaching. His process, however, was not entirely satisfactory, and,
after undergoing various modifications and improvements, it was finally
made thoroughly practicable by Mr. Tennant, who hit upon a compound of
chlorine and lime--the chloride of lime--which was a comparatively cheap
chemical product, and answered the purpose better even than chlorine
itself.

To appreciate how momentous this discovery was to cloth manufacturers,
it should be remembered that the old process of bleaching consumed an
entire summer for the whitening of a single piece of linen; the new
process reduced the period to a few hours. To be sure, lime had been
used with fair success previous to Tennant's discovery, but successful
and practical bleaching by a solution of chloride of lime was first made
possible by him and through Scheele's discovery of chlorine.

Until the time of Scheele the great subject of organic chemistry had
remained practically unexplored, but under the touch of his marvellous
inventive genius new methods of isolating and studying animal and
vegetable products were introduced, and a large number of acids and
other organic compounds prepared that had been hitherto unknown. His
explanations of chemical phenomena were based on the phlogiston theory,
in which, like Priestley, he always, believed. Although in error in
this respect, he was, nevertheless, able to make his discoveries with
extremely accurate interpretations. A brief epitome of the list of some
of his more important discoveries conveys some idea, of his fertility of
mind as well as his industry. In 1780 he discovered lactic acid,(7) and
showed that it was the substance that caused the acidity of sour
milk; and in the same year he discovered mucic acid. Next followed the
discovery of tungstic acid, and in 1783 he added to his list of useful
discoveries that of glycerine. Then in rapid succession came his
announcements of the new vegetable products citric, malic, oxalic, and
gallic acids. Scheele not only made the discoveries, but told the
world how he had made them--how any chemist might have made them if
he chose--for he never considered that he had really discovered any
substance until he had made it, decomposed it, and made it again.

His experiments on Prussian blue are most interesting, not only because
of the enormous amount of work involved and the skill he displayed in
his experiments, but because all the time the chemist was handling,
smelling, and even tasting a compound of one of the most deadly poisons,
ignorant of the fact that the substance was a dangerous one to handle.
His escape from injury seems almost miraculous; for his experiments,
which were most elaborate, extended over a considerable period of time,
during which he seems to have handled this chemical with impunity.

While only forty years of age and just at the zenith of his fame,
Scheele was stricken by a fatal illness, probably induced by his
ceaseless labor and exposure. It is gratifying to know, however, that
during the last eight or nine years of his life he had been less bound
down by pecuniary difficulties than before, as Bergman had obtained for
him an annual grant from the Academy. But it was characteristic of the
man that, while devoting one-sixth of the amount of this grant to his
personal wants, the remaining five-sixths was devoted to the expense of
his experiments.


LAVOISIER AND THE FOUNDATION OF MODERN CHEMISTRY

The time was ripe for formulating the correct theory of chemical
composition: it needed but the master hand to mould the materials into
the proper shape. The discoveries in chemistry during the eighteenth
century had been far-reaching and revolutionary in character. A brief
review of these discoveries shows how completely they had subverted
the old ideas of chemical elements and chemical compounds. Of the four
substances earth, air, fire, and water, for many centuries believed
to be elementary bodies, not one has stood the test of the
eighteenth-century chemists. Earth had long since ceased to be regarded
as an element, and water and air had suffered the same fate in this
century. And now at last fire itself, the last of the four "elements"
and the keystone to the phlogiston arch, was shown to be nothing more
than one of the manifestations of the new element, oxygen, and not
"phlogiston" or any other intangible substance.

In this epoch of chemical discoveries England had produced such mental
giants and pioneers in science as Black, Priestley, and Cavendish;
Sweden had given the world Scheele and Bergman, whose work, added to
that of their English confreres, had laid the broad base of chemistry
as a science; but it was for France to produce a man who gave the
final touches to the broad but rough workmanship of its foundation,
and establish it as the science of modern chemistry. It was for Antoine
Laurent Lavoisier (1743-1794) to gather together, interpret correctly,
rename, and classify the wealth of facts that his immediate predecessors
and contemporaries had given to the world.

The attitude of the mother-countries towards these illustrious sons is
an interesting piece of history. Sweden honored and rewarded Scheele
and Bergman for their efforts; England received the intellectuality of
Cavendish with less appreciation than the Continent, and a fanatical mob
drove Priestley out of the country; while France, by sending Lavoisier
to the guillotine, demonstrated how dangerous it was, at that time
at least, for an intelligent Frenchman to serve his fellowman and his
country well.

"The revolution brought about by Lavoisier in science," says Hoefer,
"coincides by a singular act of destiny with another revolution, much
greater indeed, going on then in the political and social world. Both
happened on the same soil, at the same epoch, among the same people;
and both marked the commencement of a new era in their respective
spheres."(8)

Lavoisier was born in Paris, and being the son of an opulent family,
was educated under the instruction of the best teachers of the day. With
Lacaille he studied mathematics and astronomy; with Jussieu, botany;
and, finally, chemistry under Rouelle. His first work of importance was
a paper on the practical illumination of the streets of Paris, for which
a prize had been offered by M. de Sartine, the chief of police. This
prize was not awarded to Lavoisier, but his suggestions were of such
importance that the king directed that a gold medal be bestowed upon the
young author at the public sitting of the Academy in April, 1776. Two
years later, at the age of thirty-five, Lavoisier was admitted a member
of the Academy.

In this same year he began to devote himself almost exclusively to
chemical inquiries, and established a laboratory in his home, fitted
with all manner of costly apparatus and chemicals. Here he was in
constant communication with the great men of science of Paris, to all of
whom his doors were thrown open. One of his first undertakings in this
laboratory was to demonstrate that water could not be converted into
earth by repeated distillations, as was generally advocated; and to show
also that there was no foundation to the existing belief that it was
possible to convert water into a gas so "elastic" as to pass through
the pores of a vessel. He demonstrated the fallaciousness of both these
theories in 1768-1769 by elaborate experiments, a single investigation
of this series occupying one hundred and one days.

In 1771 he gave the first blow to the phlogiston theory by his
experiments on the calcination of metals. It will be recalled that one
basis for the belief in phlogiston was the fact that when a metal was
calcined it was converted into an ash, giving up its "phlogiston" in the
process. To restore the metal, it was necessary to add some substance
such as wheat or charcoal to the ash. Lavoisier, in examining this
process of restoration, found that there was always evolved a great
quantity of "air," which he supposed to be "fixed air" or carbonic
acid--the same that escapes in effervescence of alkalies and calcareous
earths, and in the fermentation of liquors. He then examined the process
of calcination, whereby the phlogiston of the metal was supposed to
have been drawn off. But far from finding that phlogiston or any other
substance had been driven off, he found that something had been taken
on: that the metal "absorbed air," and that the increased weight of the
metal corresponded to the amount of air "absorbed." Meanwhile he
was within grasp of two great discoveries, that of oxygen and of the
composition of the air, which Priestley made some two years later.

The next important inquiry of this great Frenchman was as to the
composition of diamonds. With the great lens of Tschirnhausen belonging
to the Academy he succeeded in burning up several diamonds, regardless
of expense, which, thanks to his inheritance, he could ignore. In this
process he found that a gas was given off which precipitated lime from
water, and proved to be carbonic acid. Observing this, and experimenting
with other substances known to give off carbonic acid in the same
manner, he was evidently impressed with the now well-known fact that
diamond and charcoal are chemically the same. But if he did really
believe it, he was cautious in expressing his belief fully. "We should
never have expected," he says, "to find any relation between charcoal
and diamond, and it would be unreasonable to push this analogy too far;
it only exists because both substances seem to be properly ranged in the
class of combustible bodies, and because they are of all these bodies
the most fixed when kept from contact with air."

As we have seen, Priestley, in 1774, had discovered oxygen, or
"dephlogisticated air." Four years later Lavoisier first advanced his
theory that this element discovered by Priestley was the universal
acidifying or oxygenating principle, which, when combined with charcoal
or carbon, formed carbonic acid; when combined with sulphur, formed
sulphuric (or vitriolic) acid; with nitrogen, formed nitric acid,
etc., and when combined with the metals formed oxides, or calcides.
Furthermore, he postulated the theory that combustion was not due to any
such illusive thing as "phlogiston," since this did not exist, and it
seemed to him that the phenomena of combustion heretofore attributed to
phlogiston could be explained by the action of the new element oxygen
and heat. This was the final blow to the phlogiston theory, which,
although it had been tottering for some time, had not been completely
overthrown.

In 1787 Lavoisier, in conjunction with Guyon de Morveau, Berthollet,
and Fourcroy, introduced the reform in chemical nomenclature which until
then had remained practically unchanged since alchemical days. Such
expressions as "dephlogisticated" and "phlogisticated" would obviously
have little meaning to a generation who were no longer to believe in
the existence of phlogiston. It was appropriate that a revolution in
chemical thought should be accompanied by a corresponding revolution in
chemical names, and to Lavoisier belongs chiefly the credit of bringing
about this revolution. In his Elements of Chemistry he made use of this
new nomenclature, and it seemed so clearly an improvement over the
old that the scientific world hastened to adopt it. In this connection
Lavoisier says: "We have, therefore, laid aside the expression metallic
calx altogether, and have substituted in its place the word oxide. By
this it may be seen that the language we have adopted is both copious
and expressive. The first or lowest degree of oxygenation in bodies
converts them into oxides; a second degree of additional oxygenation
constitutes the class of acids of which the specific names drawn from
their particular bases terminate in ous, as in the nitrous and the
sulphurous acids. The third degree of oxygenation changes these into the
species of acids distinguished by the termination in ic, as the nitric
and sulphuric acids; and, lastly, we can express a fourth or higher
degree of oxygenation by adding the word oxygenated to the name of the
acid, as has already been done with oxygenated muriatic acid."(9)

This new work when given to the world was not merely an epoch-making
book; it was revolutionary. It not only discarded phlogiston altogether,
but set forth that metals are simple elements, not compounds of "earth"
and "phlogiston." It upheld Cavendish's demonstration that water itself,
like air, is a compound of oxygen with another element. In short, it was
scientific chemistry, in the modern acceptance of the term.

Lavoisier's observations on combustion are at once important and
interesting: "Combustion," he says, "... is the decomposition of oxygen
produced by a combustible body. The oxygen which forms the base of this
gas is absorbed by and enters into combination with the burning body,
while the caloric and light are set free. Every combustion necessarily
supposes oxygenation; whereas, on the contrary, every oxygenation
does not necessarily imply concomitant combustion; because combustion
properly so called cannot take place without disengagement of caloric
and light. Before combustion can take place, it is necessary that the
base of oxygen gas should have greater affinity to the combustible body
than it has to caloric; and this elective attraction, to use Bergman's
expression, can only take place at a certain degree of temperature which
is different for each combustible substance; hence the necessity of
giving the first motion or beginning to every combustion by the approach
of a heated body. This necessity of heating any body we mean to burn
depends upon certain considerations which have not hitherto been
attended to by any natural philosopher, for which reason I shall enlarge
a little upon the subject in this place:

"Nature is at present in a state of equilibrium, which cannot have been
attained until all the spontaneous combustions or oxygenations possible
in an ordinary degree of temperature had taken place.... To illustrate
this abstract view of the matter by example: Let us suppose the usual
temperature of the earth a little changed, and it is raised only to the
degree of boiling water; it is evident that in this case phosphorus,
which is combustible in a considerably lower degree of temperature,
would no longer exist in nature in its pure and simple state, but would
always be procured in its acid or oxygenated state, and its radical
would become one of the substances unknown to chemistry. By gradually
increasing the temperature of the earth, the same circumstance would
successively happen to all the bodies capable of combustion; and, at
the last, every possible combustion having taken place, there would
no longer exist any combustible body whatever, and every substance
susceptible of the operation would be oxygenated and consequently
incombustible.

"There cannot, therefore, exist, as far as relates to us, any
combustible body but such as are non-combustible at the ordinary
temperature of the earth, or, what is the same thing in other words,
that it is essential to the nature of every combustible body not to
possess the property of combustion unless heated, or raised to a degree
of temperature at which its combustion naturally takes place. When this
degree is once produced, combustion commences, and the caloric which
is disengaged by the decomposition of the oxygen gas keeps up the
temperature which is necessary for continuing combustion. When this is
not the case--that is, when the disengaged caloric is not sufficient
for keeping up the necessary temperature--the combustion ceases. This
circumstance is expressed in the common language by saying that a body
burns ill or with difficulty."(10)


It needed the genius of such a man as Lavoisier to complete the
refutation of the false but firmly grounded phlogiston theory, and
against such a book as his Elements of Chemistry the feeble weapons of
the supporters of the phlogiston theory were hurled in vain.

But while chemists, as a class, had become converts to the new chemistry
before the end of the century, one man, Dr. Priestley, whose work had
done so much to found it, remained unconverted. In this, as in all his
life-work, he showed himself to be a most remarkable man. Davy said of
him, a generation later, that no other person ever discovered so many
new and curious substances as he; yet to the last he was only an amateur
in science, his profession, as we know, being the ministry. There is
hardly another case in history of a man not a specialist in science
accomplishing so much in original research as did this chemist,
physiologist, electrician; the mathematician, logician, and moralist;
the theologian, mental philosopher, and political economist. He took
all knowledge for his field; but how he found time for his numberless
researches and multifarious writings, along with his every-day duties,
must ever remain a mystery to ordinary mortals.

That this marvellously receptive, flexible mind should have refused
acceptance to the clearly logical doctrines of the new chemistry seems
equally inexplicable. But so it was. To the very last, after all his
friends had capitulated, Priestley kept up the fight. From America he
sent out his last defy to the enemy, in 1800, in a brochure entitled
"The Doctrine of Phlogiston Upheld," etc. In the mind of its author it
was little less than a paean of victory; but all the world beside knew
that it was the swan-song of the doctrine of phlogiston. Despite the
defiance of this single warrior the battle was really lost and won,
and as the century closed "antiphlogistic" chemistry had practical
possession of the field.




III. CHEMISTRY SINCE THE TIME OF DALTON

JOHN DALTON AND THE ATOMIC THEORY

Small beginnings as have great endings--sometimes. As a case in
point, note what came of the small, original effort of a self-trained
back-country Quaker youth named John Dalton, who along towards the close
of the eighteenth century became interested in the weather, and was
led to construct and use a crude water-gauge to test the amount of the
rainfall. The simple experiments thus inaugurated led to no fewer than
two hundred thousand recorded observations regarding the weather,
which formed the basis for some of the most epochal discoveries in
meteorology, as we have seen. But this was only a beginning. The simple
rain-gauge pointed the way to the most important generalization of
the nineteenth century in a field of science with which, to the casual
observer, it might seem to have no alliance whatever. The wonderful
theory of atoms, on which the whole gigantic structure of modern
chemistry is founded, was the logical outgrowth, in the mind of John
Dalton, of those early studies in meteorology.

The way it happened was this: From studying the rainfall, Dalton turned
naturally to the complementary process of evaporation. He was soon led
to believe that vapor exists, in the atmosphere as an independent gas.
But since two bodies cannot occupy the same space at the same time,
this implies that the various atmospheric gases are really composed of
discrete particles. These ultimate particles are so small that we cannot
see them--cannot, indeed, more than vaguely imagine them--yet each
particle of vapor, for example, is just as much a portion of water as if
it were a drop out of the ocean, or, for that matter, the ocean itself.
But, again, water is a compound substance, for it may be separated, as
Cavendish has shown, into the two elementary substances hydrogen and
oxygen. Hence the atom of water must be composed of two lesser atoms
joined together. Imagine an atom of hydrogen and one of oxygen. Unite
them, and we have an atom of water; sever them, and the water no longer
exists; but whether united or separate the atoms of hydrogen and of
oxygen remain hydrogen and oxygen and nothing else. Differently mixed
together or united, atoms produce different gross substances; but the
elementary atoms never change their chemical nature--their distinct
personality.

It was about the year 1803 that Dalton first gained a full grasp of the
conception of the chemical atom. At once he saw that the hypothesis,
if true, furnished a marvellous key to secrets of matter hitherto
insoluble--questions relating to the relative proportions of the atoms
themselves. It is known, for example, that a certain bulk of hydrogen
gas unites with a certain bulk of oxygen gas to form water. If it be
true that this combination consists essentially of the union of atoms
one with another (each single atom of hydrogen united to a single atom
of oxygen), then the relative weights of the original masses of hydrogen
and of oxygen must be also the relative weights of each of their
respective atoms. If one pound of hydrogen unites with five and one-half
pounds of oxygen (as, according to Dalton's experiments, it did), then
the weight of the oxygen atom must be five and one-half times that of
the hydrogen atom. Other compounds may plainly be tested in the same
way. Dalton made numerous tests before he published his theory. He found
that hydrogen enters into compounds in smaller proportions than any
other element known to him, and so, for convenience, determined to take
the weight of the hydrogen atom as unity. The atomic weight of oxygen
then becomes (as given in Dalton's first table of 1803) 5.5; that of
water (hydrogen plus oxygen) being of course 6.5. The atomic weights of
about a score of substances are given in Dalton's first paper, which
was read before the Literary and Philosophical Society of Manchester,
October 21, 1803. I wonder if Dalton himself, great and acute intellect
though he had, suspected, when he read that paper, that he was
inaugurating one of the most fertile movements ever entered on in the
whole history of science?

Be that as it may, it is certain enough that Dalton's contemporaries
were at first little impressed with the novel atomic theory. Just at
this time, as it chanced, a dispute was waging in the field of chemistry
regarding a matter of empirical fact which must necessarily be settled
before such a theory as that of Dalton could even hope for a bearing.
This was the question whether or not chemical elements unite with one
another always in definite proportions. Berthollet, the great co-worker
with Lavoisier, and now the most authoritative of living chemists,
contended that substances combine in almost indefinitely graded
proportions between fixed extremes. He held that solution is really a
form of chemical combination--a position which, if accepted, left no
room for argument.

But this contention of the master was most actively disputed, in
particular by Louis Joseph Proust, and all chemists of repute were
obliged to take sides with one or the other. For a time the authority of
Berthollet held out against the facts, but at last accumulated evidence
told for Proust and his followers, and towards the close of the first
decade of our century it came to be generally conceded that chemical
elements combine with one another in fixed and definite proportions.

More than that. As the analysts were led to weigh carefully the
quantities of combining elements, it was observed that the proportions
are not only definite, but that they bear a very curious relation to one
another. If element A combines with two different proportions of element
B to form two compounds, it appears that the weight of the larger
quantity of B is an exact multiple of that of the smaller quantity. This
curious relation was noticed by Dr. Wollaston, one of the most accurate
of observers, and a little later it was confirmed by Johan Jakob
Berzelius, the great Swedish chemist, who was to be a dominating
influence in the chemical world for a generation to come. But this
combination of elements in numerical proportions was exactly what Dalton
had noticed as early as 1802, and what bad led him directly to the
atomic weights. So the confirmation of this essential point by chemists
of such authority gave the strongest confirmation to the atomic theory.

During these same years the rising authority of the French chemical
world, Joseph Louis Gay-Lussac, was conducting experiments with gases,
which he had undertaken at first in conjunction with Humboldt, but which
later on were conducted independently. In 1809, the next year after
the publication of the first volume of Dalton's New System of Chemical
Philosophy, Gay-Lussac published the results of his observations, and
among other things brought out the remarkable fact that gases, under
the same conditions as to temperature and pressure, combine always in
definite numerical proportions as to volume. Exactly two volumes of
hydrogen, for example, combine with one volume of oxygen to form water.
Moreover, the resulting compound gas always bears a simple relation to
the combining volumes. In the case just cited, the union of two volumes
of hydrogen and one of oxygen results in precisely two volumes of water
vapor.

Naturally enough, the champions of the atomic theory seized upon
these observations of Gay-Lussac as lending strong support to their
hypothesis--all of them, that is, but the curiously self-reliant and
self-sufficient author of the atomic theory himself, who declined
to accept the observations of the French chemist as valid. Yet the
observations of Gay-Lussac were correct, as countless chemists since
then have demonstrated anew, and his theory of combination by volumes
became one of the foundation-stones of the atomic theory, despite the
opposition of the author of that theory.

The true explanation of Gay-Lussac's law of combination by volumes was
thought out almost immediately by an Italian savant, Amadeo, Avogadro,
and expressed in terms of the atomic theory. The fact must be, said
Avogadro, that under similar physical conditions every form of gas
contains exactly the same number of ultimate particles in a given
volume. Each of these ultimate physical particles may be composed of two
or more atoms (as in the case of water vapor), but such a compound atom
conducts itself as if it were a simple and indivisible atom, as regards
the amount of space that separates it from its fellows under given
conditions of pressure and temperature. The compound atom, composed
of two or more elementary atoms, Avogadro proposed to distinguish, for
purposes of convenience, by the name molecule. It is to the molecule,
considered as the unit of physical structure, that Avogadro's law
applies.

This vastly important distinction between atoms and molecules, implied
in the law just expressed, was published in 1811. Four years later, the
famous French physicist Ampere outlined a similar theory, and utilized
the law in his mathematical calculations. And with that the law of
Avogadro dropped out of sight for a full generation. Little suspecting
that it was the very key to the inner mysteries of the atoms for which
they were seeking, the chemists of the time cast it aside, and let it
fade from the memory of their science.

This, however, was not strange, for of course the law of Avogadro is
based on the atomic theory, and in 1811 the atomic theory was itself
still being weighed in the balance. The law of multiple proportions
found general acceptance as an empirical fact; but many of the leading
lights of chemistry still looked askance at Dalton's explanation of this
law. Thus Wollaston, though from the first he inclined to acceptance of
the Daltonian view, cautiously suggested that it would be well to use
the non-committal word "equivalent" instead of "atom"; and Davy, for
a similar reason, in his book of 1812, speaks only of "proportions,"
binding himself to no theory as to what might be the nature of these
proportions.

At least two great chemists of the time, however, adopted the atomic
view with less reservation. One of these was Thomas Thomson, professor
at Edinburgh, who, in 1807, had given an outline of Dalton's theory in
a widely circulated book, which first brought the theory to the general
attention of the chemical world. The other and even more noted advocate
of the atomic theory was Johan Jakob Berzelius. This great Swedish
chemist at once set to work to put the atomic theory to such tests as
might be applied in the laboratory. He was an analyst of the utmost
skill, and for years he devoted himself to the determination of the
combining weights, "equivalents" or "proportions," of the different
elements. These determinations, in so far as they were accurately made,
were simple expressions of empirical facts, independent of any theory;
but gradually it became more and more plain that these facts all
harmonize with the atomic theory of Dalton. So by common consent the
proportionate combining weights of the elements came to be known as
atomic weights--the name Dalton had given them from the first--and
the tangible conception of the chemical atom as a body of definite
constitution and weight gained steadily in favor.

From the outset the idea had had the utmost tangibility in the mind of
Dalton. He had all along represented the different atoms by geometrical
symbols--as a circle for oxygen, a circle enclosing a dot for hydrogen,
and the like--and had represented compounds by placing these symbols of
the elements in juxtaposition. Berzelius proposed to improve upon this
method by substituting for the geometrical symbol the initial of the
Latin name of the element represented--O for oxygen, H for hydrogen, and
so on--a numerical coefficient to follow the letter as an indication of
the number of atoms present in any given compound. This simple system
soon gained general acceptance, and with slight modifications it is
still universally employed. Every school-boy now is aware that H2O is
the chemical way of expressing the union of two atoms of hydrogen with
one of oxygen to form a molecule of water. But such a formula would have
had no meaning for the wisest chemist before the day of Berzelius.

The universal fame of the great Swedish authority served to give general
currency to his symbols and atomic weights, and the new point of view
thus developed led presently to two important discoveries which removed
the last lingering doubts as to the validity of the atomic theory. In
1819 two French physicists, Dulong and Petit, while experimenting with
heat, discovered that the specific heats of solids (that is to say, the
amount of heat required to raise the temperature of a given mass to a
given degree) vary inversely as their atomic weights. In the same year
Eilhard Mitscherlich, a German investigator, observed that compounds
having the same number of atoms to the molecule are disposed to form the
same angles of crystallization--a property which he called isomorphism.

Here, then, were two utterly novel and independent sets of empirical
facts which harmonize strangely with the supposition that substances are
composed of chemical atoms of a determinate weight. This surely could
not be coincidence--it tells of law. And so as soon as the claims of
Dulong and Petit and of Mitscherlich had been substantiated by other
observers, the laws of the specific heat of atoms, and of isomorphism,
took their place as new levers of chemical science. With the aid of
these new tools an impregnable breastwork of facts was soon piled about
the atomic theory. And John Dalton, the author of that theory, plain,
provincial Quaker, working on to the end in semi-retirement, became
known to all the world and for all time as a master of masters.


HUMPHRY DAVY AND ELECTRO-CHEMISTRY

During those early years of the nineteenth century, when Dalton was
grinding away at chemical fact and theory in his obscure Manchester
laboratory, another Englishman held the attention of the chemical world
with a series of the most brilliant and widely heralded researches. This
was Humphry Davy, a young man who had conic to London in 1801, at the
instance of Count Rumford, to assume the chair of chemical philosophy in
the Royal Institution, which the famous American had just founded.

Here, under Davy's direction, the largest voltaic battery yet
constructed had been put in operation, and with its aid the brilliant
young experimenter was expected almost to perform miracles. And indeed
he scarcely disappointed the expectation, for with the aid of his
battery he transformed so familiar a substance as common potash into
a metal which was not only so light that it floated on water, but
possessed the seemingly miraculous property of bursting into flames as
soon as it came in contact with that fire-quenching liquid. If this
were not a miracle, it had for the popular eye all the appearance of the
miraculous.

What Davy really had done was to decompose the potash, which hitherto
had been supposed to be elementary, liberating its oxygen, and thus
isolating its metallic base, which he named potassium. The same
thing was done with soda, and the closely similar metal sodium was
discovered--metals of a unique type, possessed of a strange avidity for
oxygen, and capable of seizing on it even when it is bound up in the
molecules of water. Considered as mere curiosities, these discoveries
were interesting, but aside from that they were of great theoretical
importance, because they showed the compound nature of some familiar
chemicals that had been regarded as elements. Several other elementary
earths met the same fate when subjected to the electrical influence; the
metals barium, calcium, and strontium being thus discovered. Thereafter
Davy always referred to the supposed elementary substances (including
oxygen, hydrogen, and the rest) as "unde-compounded" bodies. These
resist all present efforts to decompose them, but how can one know what
might not happen were they subjected to an influence, perhaps some day
to be discovered, which exceeds the battery in power as the battery
exceeds the blowpipe?

Another and even more important theoretical result that flowed from
Davy's experiments during this first decade of the century was the
proof that no elementary substances other than hydrogen and oxygen are
produced when pure water is decomposed by the electric current. It was
early noticed by Davy and others that when a strong current is passed
through water, alkalies appear at one pole of the battery and acids at
the other, and this though the water used were absolutely pure. This
seemingly told of the creation of elements--a transmutation but one step
removed from the creation of matter itself--under the influence of the
new "force." It was one of Davy's greatest triumphs to prove, in the
series of experiments recorded in his famous Bakerian lecture of 1806,
that the alleged creation of elements did not take place, the substances
found at the poles of the battery having been dissolved from the walls
of the vessels in which the water experimented upon had been placed.
Thus the same implement which had served to give a certain philosophical
warrant to the fading dreams of alchemy banished those dreams
peremptorily from the domain of present science.

"As early as 1800," writes Davy, "I had found that when separate
portions of distilled water, filling two glass tubes, connected by moist
bladders, or any moist animal or vegetable substances, were submitted
to the electrical action of the pile of Volta by means of gold wires,
a nitro-muriatic solution of gold appeared in the tube containing the
positive wire, or the wire transmitting the electricity, and a solution
of soda in the opposite tube; but I soon ascertained that the muriatic
acid owed its existence to the animal or vegetable matters employed;
for when the same fibres of cotton were made use of in successive
experiments, and washed after every process in a weak solution of nitric
acid, the water in the apparatus containing them, though acted on for
a great length of time with a very strong power, at last produced no
effects upon nitrate of silver.

"In cases when I had procured much soda, the glass at its point of
contact with the wire seemed considerably corroded; and I was confirmed
in my idea of referring the production of the alkali principally to
this source, by finding that no fixed saline matter could be obtained
by electrifying distilled water in a single agate cup from two points of
platina with the Voltaic battery.

"Mr. Sylvester, however, in a paper published in Mr. Nicholson's journal
for last August, states that though no fixed alkali or muriatic acid
appears when a single vessel is employed, yet that they are both formed
when two vessels are used. And to do away with all objections with
regard to vegetable substances or glass, he conducted his process in
a vessel made of baked tobacco-pipe clay inserted in a crucible of
platina. I have no doubt of the correctness of his results; but the
conclusion appears objectionable. He conceives, that he obtained fixed
alkali, because the fluid after being heated and evaporated left a
matter that tinged turmeric brown, which would have happened had it
been lime, a substance that exists in considerable quantities in all
pipe-clay; and even allowing the presence of fixed alkali, the materials
employed for the manufacture of tobacco-pipes are not at all such as to
exclude the combinations of this substance.

"I resumed the inquiry; I procured small cylindrical cups of agate of
the capacity of about one-quarter of a cubic inch each. They were
boiled for some hours in distilled water, and a piece of very white and
transparent amianthus that had been treated in the same way was made
then to connect together; they were filled with distilled water and
exposed by means of two platina wires to a current of electricity, from
one hundred and fifty pairs of plates of copper and zinc four inches
square, made active by means of solution of alum. After forty-eight
hours the process was examined: Paper tinged with litmus plunged into
the tube containing the transmitting or positive wire was immediately
strongly reddened. Paper colored by turmeric introduced into the other
tube had its color much deepened; the acid matter gave a very slight
degree of turgidness to solution of nitrate of soda. The fluid that
affected turmeric retained this property after being strongly
boiled; and it appeared more vivid as the quantity became reduced by
evaporation; carbonate of ammonia was mixed with it, and the whole
dried and exposed to a strong heat; a minute quantity of white matter
remained, which, as far as my examinations could go, had the properties
of carbonate of soda. I compared it with similar minute portions of
the pure carbonates of potash, and similar minute portions of the pure
carbonates of potash and soda. It was not so deliquescent as the former
of these bodies, and it formed a salt with nitric acid, which, like
nitrate of soda, soon attracted moisture from a damp atmosphere and
became fluid.

"This result was unexpected, but it was far from convincing me that the
substances which were obtained were generated. In a similar process with
glass tubes, carried on under exactly the same circumstances and for
the same time, I obtained a quantity of alkali which must have been more
than twenty times greater, but no traces of muriatic acid. There was
much probability that the agate contained some minute portion of saline
matter, not easily detected by chemical analysis, either in combination
or intimate cohesion in its pores. To determine this, I repeated this a
second, a third, and a fourth time. In the second experiment turbidness
was still produced by a solution of nitrate of silver in the tube
containing the acid, but it was less distinct; in the third process
it was barely perceptible; and in the fourth process the two fluids
remained perfectly clear after the mixture. The quantity of alkaline
matter diminished in every operation; and in the last process, though
the battery had been kept in great activity for three days, the fluid
possessed, in a very slight degree, only the power of acting on paper
tinged with turmeric; but its alkaline property was very sensible to
litmus paper slightly reddened, which is a much more delicate test;
and after evaporation and the process by carbonate of ammonia, a barely
perceptible quantity of fixed alkali was still left. The acid matter in
the other tube was abundant; its taste was sour; it smelled like water
over which large quantities of nitrous gas have been long kept; it did
not effect solution of muriate of barytes; and a drop of it placed
upon a polished plate of silver left, after evaporation, a black stain,
precisely similar to that produced by extremely diluted nitrous acid.

"After these results I could no longer doubt that some saline matter
existing in the agate tubes had been the source of the acid matter
capable of precipitating nitrate of silver and much of the alkali. Four
additional repetitions of the process, however, convinced me that there
was likewise some other cause for the presence of this last substance;
for it continued to appear to the last in quantities sufficiently
distinguishable, and apparently equal in every case. I had used every
precaution, I had included the tube in glass vessels out of the reach of
the circulating air; all the acting materials had been repeatedly washed
with distilled water; and no part of them in contact with the fluid had
been touched by the fingers.

"The only substance that I could now conceive as furnishing the fixed
alkali was the water itself. This water appeared pure by the tests of
nitrate of silver and muriate of barytes; but potash of soda, as is
well known, rises in small quantities in rapid distillation; and the
New River water which I made use of contains animal and vegetable
impurities, which it was easy to conceive might furnish neutral
salts capable of being carried over in vivid ebullition."(1) Further
experiment proved the correctness of this inference, and the last doubt
as to the origin of the puzzling chemical was dispelled.

Though the presence of the alkalies and acids in the water was
explained, however, their respective migrations to the negative and
positive poles of the battery remained to be accounted for. Davy's
classical explanation assumed that different elements differ among
themselves as to their electrical properties, some being positively,
others negatively, electrified. Electricity and "chemical affinity," he
said, apparently are manifestations of the same force, acting in the one
case on masses, in the other on particles. Electro-positive particles
unite with electro-negative particles to form chemical compounds, in
virtue of the familiar principle that opposite electricities attract
one another. When compounds are decomposed by the battery, this mutual
attraction is overcome by the stronger attraction of the poles of the
battery itself.

This theory of binary composition of all chemical compounds, through the
union of electro-positive and electro-negative atoms or molecules,
was extended by Berzelius, and made the basis of his famous system of
theoretical chemistry. This theory held that all inorganic compounds,
however complex their composition, are essentially composed of such
binary combinations. For many years this view enjoyed almost undisputed
sway. It received what seemed strong confirmation when Faraday showed
the definite connection between the amount of electricity employed and
the amount of decomposition produced in the so-called electrolyte. But
its claims were really much too comprehensive, as subsequent discoveries
proved.


ORGANIC CHEMISTRY AND THE IDEA OF THE MOLECULE

When Berzelius first promulgated his binary theory he was careful to
restrict its unmodified application to the compounds of the inorganic
world. At that time, and for a long time thereafter, it was supposed
that substances of organic nature had some properties that kept them
aloof from the domain of inorganic chemistry. It was little doubted
that a so-called "vital force" operated here, replacing or modifying the
action of ordinary "chemical affinity." It was, indeed, admitted that
organic compounds are composed of familiar elements--chiefly carbon,
oxygen, hydrogen, and nitrogen; but these elements were supposed to
be united in ways that could not be imitated in the domain of the
non-living. It was regarded almost as an axiom of chemistry that
no organic compound whatever could be put together from its
elements--synthesized--in the laboratory. To effect the synthesis of
even the simplest organic compound, it was thought that the "vital
force" must be in operation.

Therefore a veritable sensation was created in the chemical world
when, in the year 1828, it was announced that the young German chemist,
Friedrich Wohler, formerly pupil of Berzelius, and already known as a
coming master, had actually synthesized the well-known organic product
urea in his laboratory at Sacrow. The "exception which proves the rule"
is something never heard of in the domain of logical science. Natural
law knows no exceptions. So the synthesis of a single organic compound
sufficed at a blow to break down the chemical barrier which the
imagination of the fathers of the science had erected between animate
and inanimate nature. Thenceforth the philosophical chemist would
regard the plant and animal organisms as chemical laboratories in which
conditions are peculiarly favorable for building up complex compounds of
a few familiar elements, under the operation of universal chemical laws.
The chimera "vital force" could no longer gain recognition in the domain
of chemistry.

Now a wave of interest in organic chemistry swept over the chemical
world, and soon the study of carbon compounds became as much the fashion
as electrochemistry had been in the, preceding generation.

Foremost among the workers who rendered this epoch of organic chemistry
memorable were Justus Liebig in Germany and Jean Baptiste Andre Dumas
in France, and their respective pupils, Charles Frederic Gerhardt and
Augustus Laurent. Wohler, too, must be named in the same breath, as also
must Louis Pasteur, who, though somewhat younger than the others, came
upon the scene in time to take chief part in the most important of the
controversies that grew out of their labors.

Several years earlier than this the way had been paved for the study
of organic substances by Gay-Lussac's discovery, made in 1815, that a
certain compound of carbon and nitrogen, which he named cyanogen, has a
peculiar degree of stability which enables it to retain its identity and
enter into chemical relations after the manner of a simple body. A year
later Ampere discovered that nitrogen and hydrogen, when combined in
certain proportions to form what he called ammonium, have the same
property. Berzelius had seized upon this discovery of the compound
radical, as it was called, because it seemed to lend aid to his
dualistic theory. He conceived the idea that all organic compounds
are binary unions of various compound radicals with an atom of oxygen,
announcing this theory in 1818. Ten years later, Liebig and Wohler
undertook a joint investigation which resulted in proving that compound
radicals are indeed very abundant among organic substances. Thus the
theory of Berzelius seemed to be substantiated, and organic chemistry
came to be defined as the chemistry of compound radicals.

But even in the day of its seeming triumph the dualistic theory
was destined to receive a rude shock. This came about through the
investigations of Dumas, who proved that in a certain organic substance
an atom of hydrogen may be removed and an atom of chlorine substituted
in its place without destroying the integrity of the original
compound--much as a child might substitute one block for another in
its play-house. Such a substitution would be quite consistent with the
dualistic theory, were it not for the very essential fact that hydrogen
is a powerfully electro-positive element, while chlorine is as strongly
electro-negative. Hence the compound radical which united successively
with these two elements must itself be at one time electro-positive, at
another electro-negative--a seeming inconsistency which threw the entire
Berzelian theory into disfavor.

In its place there was elaborated, chiefly through the efforts of
Laurent and Gerhardt, a conception of the molecule as a unitary
structure, built up through the aggregation of various atoms, in
accordance with "elective affinities" whose nature is not yet understood
A doctrine of "nuclei" and a doctrine of "types" of molecular structure
were much exploited, and, like the doctrine of compound radicals, became
useful as aids to memory and guides for the analyst, indicating some of
the plans of molecular construction, though by no means penetrating the
mysteries of chemical affinity. They are classifications rather than
explanations of chemical unions. But at least they served an important
purpose in giving definiteness to the idea of a molecular structure
built of atoms as the basis of all substances. Now at last the word
molecule came to have a distinct meaning, as distinct from "atom," in
the minds of the generality of chemists, as it had had for Avogadro a
third of a century before. Avogadro's hypothesis that there are equal
numbers of these molecules in equal volumes of gases, under fixed
conditions, was revived by Gerhardt, and a little later, under the
championship of Cannizzaro, was exalted to the plane of a fixed law.
Thenceforth the conception of the molecule was to be as dominant a
thought in chemistry as the idea of the atom had become in a previous
epoch.


CHEMICAL AFFINITY

Of course the atom itself was in no sense displaced, but Avogadro's law
soon made it plain that the atom had often usurped territory that
did not really belong to it. In many cases the chemists had supposed
themselves dealing with atoms as units where the true unit was the
molecule. In the case of elementary gases, such as hydrogen and oxygen,
for example, the law of equal numbers of molecules in equal spaces made
it clear that the atoms do not exist isolated, as had been supposed.
Since two volumes of hydrogen unite with one volume of oxygen to form
two volumes of water vapor, the simplest mathematics show, in the light
of Avogadro's law, not only that each molecule of water must contain two
hydrogen atoms (a point previously in dispute), but that the original
molecules of hydrogen and oxygen must have been composed in each case of
two atoms---else how could one volume of oxygen supply an atom for every
molecule of two volumes of water?

What, then, does this imply? Why, that the elementary atom has
an avidity for other atoms, a longing for companionship, an
"affinity"--call it what you will--which is bound to be satisfied if
other atoms are in the neighborhood. Placed solely among atoms of its
own kind, the oxygen atom seizes on a fellow oxygen atom, and in all
their mad dancings these two mates cling together--possibly revolving
about each other in miniature planetary orbits. Precisely the same thing
occurs among the hydrogen atoms. But now suppose the various pairs
of oxygen atoms come near other pairs of hydrogen atoms (under proper
conditions which need not detain us here), then each oxygen atom loses
its attachment for its fellow, and flings itself madly into the circuit
of one of the hydrogen couplets, and--presto!--there are only two
molecules for every three there were before, and free oxygen and
hydrogen have become water. The whole process, stated in chemical
phraseology, is summed up in the statement that under the given
conditions the oxygen atoms had a greater affinity for the hydrogen
atoms than for one another.

As chemists studied the actions of various kinds of atoms, in regard
to their unions with one another to form molecules, it gradually dawned
upon them that not all elements are satisfied with the same number of
companions. Some elements ask only one, and refuse to take more; while
others link themselves, when occasion offers, with two, three, four, or
more. Thus we saw that oxygen forsook a single atom of its own kind
and linked itself with two atoms of hydrogen. Clearly, then, the oxygen
atom, like a creature with two hands, is able to clutch two other atoms.
But we have no proof that under any circumstances it could hold more
than two. Its affinities seem satisfied when it has two bonds. But,
on the other hand, the atom of nitrogen is able to hold three atoms
of hydrogen, and does so in the molecule of ammonium (NH3); while the
carbon atom can hold four atoms of hydrogen or two atoms of oxygen.

Evidently, then, one atom is not always equivalent to another atom of
a different kind in combining powers. A recognition of this fact by
Frankland about 1852, and its further investigation by others (notably
A. Kekule and A. S. Couper), led to the introduction of the word
equivalent into chemical terminology in a new sense, and in particular
to an understanding of the affinities or "valency" of different
elements, which proved of the most fundamental importance. Thus it
was shown that, of the four elements that enter most prominently into
organic compounds, hydrogen can link itself with only a single bond to
any other element--it has, so to speak, but a single hand with which
to grasp--while oxygen has capacity for two bonds, nitrogen for
three (possibly for five), and carbon for four. The words monovalent,
divalent, trivalent, tretrava-lent, etc., were coined to express this
most important fact, and the various elements came to be known as
monads, diads, triads, etc. Just why different elements should differ
thus in valency no one as yet knows; it is an empirical fact that they
do. And once the nature of any element has been determined as regards
its valency, a most important insight into the possible behavior of that
element has been secured. Thus a consideration of the fact that hydrogen
is monovalent, while oxygen is divalent, makes it plain that we
must expect to find no more than three compounds of these two
elements--namely, H--O--(written HO by the chemist, and called
hydroxyl); H--O--H (H2O, or water), and H--O--O--H (H2O2, or hydrogen
peroxide). It will be observed that in the first of these compounds the
atom of oxygen stands, so to speak, with one of its hands free, eagerly
reaching out, therefore, for another companion, and hence, in the
language of chemistry, forming an unstable compound. Again, in the third
compound, though all hands are clasped, yet one pair links oxygen with
oxygen; and this also must be an unstable union, since the avidity of an
atom for its own kind is relatively weak. Thus the well-known properties
of hydrogen peroxide are explained, its easy decomposition, and the
eagerness with which it seizes upon the elements of other compounds.

But the molecule of water, on the other hand, has its atoms arranged
in a state of stable equilibrium, all their affinities being satisfied.
Each hydrogen atom has satisfied its own affinity by clutching the
oxygen atom; and the oxygen atom has both its bonds satisfied by
clutching back at the two hydrogen atoms. Therefore the trio, linked in
this close bond, have no tendency to reach out for any other companion,
nor, indeed, any power to hold another should it thrust itself
upon them. They form a "stable" compound, which under all ordinary
circumstances will retain its identity as a molecule of water, even
though the physical mass of which it is a part changes its condition
from a solid to a gas from ice to vapor.

But a consideration of this condition of stable equilibrium in the
molecule at once suggests a new question: How can an aggregation of
atoms, having all their affinities satisfied, take any further part in
chemical reactions? Seemingly such a molecule, whatever its physical
properties, must be chemically inert, incapable of any atomic
readjustments. And so in point of fact it is, so long as its component
atoms cling to one another unremittingly. But this, it appears, is
precisely what the atoms are little prone to do. It seems that they are
fickle to the last degree in their individual attachments, and are as
prone to break away from bondage as they are to enter into it. Thus the
oxygen atom which has just flung itself into the circuit of two
hydrogen atoms, the next moment flings itself free again and seeks
new companions. It is for all the world like the incessant change
of partners in a rollicking dance. This incessant dissolution and
reformation of molecules in a substance which as a whole remains
apparently unchanged was first fully appreciated by Ste.-Claire Deville,
and by him named dissociation. It is a process which goes on much more
actively in some compounds than in others, and very much more actively
under some physical conditions (such as increase of temperature) than
under others. But apparently no substances at ordinary temperatures,
and no temperature above the absolute zero, are absolutely free from its
disturbing influence. Hence it is that molecules having all the
valency of their atoms fully satisfied do not lose their chemical
activity--since each atom is momentarily free in the exchange of
partners, and may seize upon different atoms from its former partners,
if those it prefers are at hand.

While, however, an appreciation of this ceaseless activity of the atom
is essential to a proper understanding of its chemical efficiency,
yet from another point of view the "saturated" molecule--that is, the
molecule whose atoms have their valency all satisfied--may be thought of
as a relatively fixed or stable organism. Even though it may presently
be torn down, it is for the time being a completed structure; and a
consideration of the valency of its atoms gives the best clew that has
hitherto been obtainable as to the character of its architecture.
How important this matter of architecture of the molecule--of space
relations of the atoms--may be--was demonstrated as long ago as 1823,
when Liebig and Wohler proved, to the utter bewilderment of the
chemical world, that two substances may have precisely the same chemical
constitution--the same number and kind of atoms--and yet differ utterly
in physical properties. The word isomerism was coined by Berzelius to
express this anomalous condition of things, which seemed to negative the
most fundamental truths of chemistry. Naming the condition by no means
explained it, but the fact was made clear that something besides the
mere number and kind of atoms is important in the architecture of a
molecule. It became certain that atoms are not thrown together haphazard
to build a molecule, any more than bricks are thrown together at random
to form a house.

How delicate may be the gradations of architectural design in building
a molecule was well illustrated about 1850, when Pasteur discovered that
some carbon compounds--as certain sugars--can only be distinguished
from one another, when in solution, by the fact of their twisting or
polarizing a ray of light to the left or to the right, respectively. But
no inkling of an explanation of these strange variations of molecular
structure came until the discovery of the law of valency. Then much of
the mystery was cleared away; for it was plain that since each atom in a
molecule can hold to itself only a fixed number of other atoms, complex
molecules must have their atoms linked in definite chains or groups. And
it is equally plain that where the atoms are numerous, the exact plan of
grouping may sometimes be susceptible of change without doing violence
to the law of valency. It is in such cases that isomerism is observed to
occur.

By paying constant heed to this matter of the affinities, chemists are
able to make diagrammatic pictures of the plan of architecture of any
molecule whose composition is known. In the simple molecule of water
(H2O), for example, the two hydrogen atoms must have released each
other before they could join the oxygen, and the manner of linking must
apparently be that represented in the graphic formula H--O--H.
With molecules composed of a large number of atoms, such graphic
representation of the scheme of linking is of course increasingly
difficult, yet, with the affinities for a guide, it is always possible.
Of course no one supposes that such a formula, written in a single
plane, can possibly represent the true architecture of the molecule:
it is at best suggestive or diagrammatic rather than pictorial.
Nevertheless, it affords hints as to the structure of the molecule such
as the fathers of chemistry would not have thought it possible ever to
attain.


PERIODICITY OF ATOMIC WEIGHTS

These utterly novel studies of molecular architecture may seem at
first sight to take from the atom much of its former prestige as the
all-important personage of the chemical world. Since so much depends
upon the mere position of the atoms, it may appear that comparatively
little depends upon the nature of the atoms themselves. But such a view
is incorrect, for on closer consideration it will appear that at no
time has the atom been seen to renounce its peculiar personality. Within
certain limits the character of a molecule may be altered by changing
the positions of its atoms (just as different buildings may be
constructed of the same bricks), but these limits are sharply defined,
and it would be as impossible to exceed them as it would be to build
a stone building with bricks. From first to last the brick remains a
brick, whatever the style of architecture it helps to construct; it
never becomes a stone. And just as closely does each atom retain its own
peculiar properties, regardless of its surroundings.

Thus, for example, the carbon atom may take part in the formation at one
time of a diamond, again of a piece of coal, and yet again of a
particle of sugar, of wood fibre, of animal tissue, or of a gas in the
atmosphere; but from first to last--from glass-cutting gem to intangible
gas--there is no demonstrable change whatever in any single property of
the atom itself. So far as we know, its size, its weight, its capacity
for vibration or rotation, and its inherent affinities, remain
absolutely unchanged throughout all these varying fortunes of position
and association. And the same thing is true of every atom of all of
the seventy-odd elementary substances with which the modern chemist is
acquainted. Every one appears always to maintain its unique integrity,
gaining nothing and losing nothing.

All this being true, it would seem as if the position of the Daltonian
atom as a primordial bit of matter, indestructible and non-transmutable,
had been put to the test by the chemistry of our century, and not found
wanting. Since those early days of the century when the electric battery
performed its miracles and seemingly reached its limitations in the
hands of Davy, many new elementary substances have been discovered,
but no single element has been displaced from its position as an
undecomposable body. Rather have the analyses of the chemist seemed to
make it more and more certain that all elementary atoms are in truth
what John Herschel called them, "manufactured articles"--primordial,
changeless, indestructible.

And yet, oddly enough, it has chanced that hand in hand with the
experiments leading to such a goal have gone other experiments arid
speculations of exactly the opposite tenor. In each generation there
have been chemists among the leaders of their science who have refused
to admit that the so-called elements are really elements at all in any
final sense, and who have sought eagerly for proof which might warrant
their scepticism. The first bit of evidence tending to support this view
was furnished by an English physician, Dr. William Prout, who in 1815
called attention to a curious relation to be observed between the atomic
weight of the various elements. Accepting the figures given by the
authorities of the time (notably Thomson and Berzelius), it appeared
that a strikingly large proportion of the atomic weights were exact
multiples of the weight of hydrogen, and that others differed so
slightly that errors of observation might explain the discrepancy. Prout
felt that it could not be accidental, and he could think of no tenable
explanation, unless it be that the atoms of the various alleged elements
are made up of different fixed numbers of hydrogen atoms. Could it be
that the one true element--the one primal matter--is hydrogen, and that
all other forms of matter are but compounds of this original substance?

Prout advanced this startling idea at first tentatively, in an anonymous
publication; but afterwards he espoused it openly and urged its
tenability. Coming just after Davy's dissociation of some supposed
elements, the idea proved alluring, and for a time gained such
popularity that chemists were disposed to round out the observed atomic
weights of all elements into whole numbers. But presently renewed
determinations of the atomic weights seemed to discountenance this
practice, and Prout's alleged law fell into disrepute. It was revived,
however, about 1840, by Dumas, whose great authority secured it a
respectful hearing, and whose careful redetermination of the weight
of carbon, making it exactly twelve times that of hydrogen, aided the
cause.

Subsequently Stas, the pupil of Dumas, undertook a long series of
determinations of atomic weights, with the expectation of confirming the
Proutian hypothesis. But his results seemed to disprove the hypothesis,
for the atomic weights of many elements differed from whole numbers by
more, it was thought, than the limits of error of the experiments. It
was noteworthy, however, that the confidence of Dumas was not shaken,
though he was led to modify the hypothesis, and, in accordance with
previous suggestions of Clark and of Marignac, to recognize as the
primordial element, not hydrogen itself, but an atom half the weight,
or even one-fourth the weight, of that of hydrogen, of which primordial
atom the hydrogen atom itself is compounded. But even in this modified
form the hypothesis found great opposition from experimental observers.

In 1864, however, a novel relation between the weights of the elements
and their other characteristics was called to the attention of chemists
by Professor John A. R. Newlands, of London, who had noticed that if the
elements are arranged serially in the numerical order of their atomic
weights, there is a curious recurrence of similar properties at
intervals of eight elements This so-called "law of octaves" attracted
little immediate attention, but the facts it connotes soon came under
the observation of other chemists, notably of Professors Gustav Hinrichs
in America, Dmitri Mendeleeff in Russia, and Lothar Meyer in Germany.
Mendeleeff gave the discovery fullest expression, explicating it in
1869, under the title of "the periodic law."

Though this early exposition of what has since been admitted to be a
most important discovery was very fully outlined, the generality of
chemists gave it little heed till a decade or so later, when three new
elements, gallium, scandium, and germanium, were discovered, which, on
being analyzed, were quite unexpectedly found to fit into three gaps
which Mendeleeff had left in his periodic scale. In effect the periodic
law had enabled Mendeleeff to predicate the existence of the new
elements years before they were discovered. Surely a system that leads
to such results is no mere vagary. So very soon the periodic law took
its place as one of the most important generalizations of chemical
science.

This law of periodicity was put forward as an expression of observed
relations independent of hypothesis; but of course the theoretical
bearings of these facts could not be overlooked. As Professor J. H.
Gladstone has said, it forces upon us "the conviction that the elements
are not separate bodies created without reference to one another, but
that they have been originally fashioned, or have been built up, from
one another, according to some general plan." It is but a short step
from that proposition to the Proutian hypothesis.


NEW WEAPONS--SPECTROSCOPE AND CAMERA

But the atomic weights are not alone in suggesting the compound nature
of the alleged elements. Evidence of a totally different kind has
contributed to the same end, from a source that could hardly have been
imagined when the Proutian hypothesis, was formulated, through the
tradition of a novel weapon to the armamentarium of the chemist--the
spectroscope. The perfection of this instrument, in the hands of two
German scientists, Gustav Robert Kirchhoff and Robert Wilhelm Bunsen,
came about through the investigation, towards the middle of the century,
of the meaning of the dark lines which had been observed in the solar
spectrum by Fraunhofer as early as 1815, and by Wollaston a decade
earlier. It was suspected by Stokes and by Fox Talbot in England, but
first brought to demonstration by Kirchhoff and Bunsen, that these
lines, which were known to occupy definite positions in the spectrum,
are really indicative of particular elementary substances. By means of
the spectroscope, which is essentially a magnifying lens attached to a
prism of glass, it is possible to locate the lines with great accuracy,
and it was soon shown that here was a new means of chemical analysis
of the most exquisite delicacy. It was found, for example, that the
spectroscope could detect the presence of a quantity of sodium so
infinitesimal as the one two-hundred-thousandth of a grain. But what was
even more important, the spectroscope put no limit upon the distance of
location of the substance it tested, provided only that sufficient light
came from it. The experiments it recorded might be performed in the sun,
or in the most distant stars or nebulae; indeed, one of the earliest
feats of the instrument was to wrench from the sun the secret of his
chemical constitution.

To render the utility of the spectroscope complete, however, it
was necessary to link with it another new chemical agency--namely,
photography. This now familiar process is based on the property of light
to decompose certain unstable compounds of silver, and thus alter their
chemical composition. Davy and Wedgwood barely escaped the discovery of
the value of the photographic method early in the nineteenth century.
Their successors quite overlooked it until about 1826, when Louis J. M.
Daguerre, the French chemist, took the matter in hand, and after many
years of experimentation brought it to relative perfection in 1839, in
which year the famous daguerreotype first brought the matter to popular
attention. In the same year Mr. Fox Talbot read a paper on the subject
before the Royal Society, and soon afterwards the efforts of Herschel
and numerous other natural philosophers contributed to the advancement
of the new method.

In 1843 Dr. John W. Draper, the famous English-American chemist and
physiologist, showed that by photography the Fraunhofer lines in the
solar spectrum might be mapped with absolute accuracy; also proving that
the silvered film revealed many lines invisible to the unaided eye. The
value of this method of observation was recognized at once, and, as
soon as the spectroscope was perfected, the photographic method, in
conjunction with its use, became invaluable to the chemist. By this
means comparisons of spectra may be made with a degree of accuracy
not otherwise obtainable; and, in case of the stars, whole clusters of
spectra may be placed on record at a single observation.

As the examination of the sun and stars proceeded, chemists were amazed
or delighted, according to their various preconceptions, to witness the
proof that many familiar terrestrial elements are to be found in the
celestial bodies. But what perhaps surprised them most was to observe
the enormous preponderance in the sidereal bodies of the element
hydrogen. Not only are there vast quantities of this element in the
sun's atmosphere, but some other suns appeared to show hydrogen lines
almost exclusively in their spectra. Presently it appeared that the
stars of which this is true are those white stars, such as Sirius, which
had been conjectured to be the hottest; whereas stars that are only
red-hot, like our sun, show also the vapors of many other elements,
including iron and other metals.

In 1878 Professor J. Norman Lockyer, in a paper before the Royal
Society, called attention to the possible significance of this series of
observations. He urged that the fact of the sun showing fewer elements
than are observed here on the cool earth, while stars much hotter than
the sun show chiefly one element, and that one hydrogen, the lightest of
known elements, seemed to give color to the possibility that our alleged
elements are really compounds, which at the temperature of the hottest
stars may be decomposed into hydrogen, the latter "element" itself being
also doubtless a compound, which might be resolved under yet more trying
conditions.

Here, then, was what might be termed direct experimental evidence for
the hypothesis of Prout. Unfortunately, however, it is evidence of a
kind which only a few experts are competent to discuss--so very delicate
a matter is the spectral analysis of the stars. What is still more
unfortunate, the experts do not agree among themselves as to the
validity of Professor Lockyer's conclusions. Some, like Professor
Crookes, have accepted them with acclaim, hailing Lockyer as "the
Darwin of the inorganic world," while others have sought a different
explanation of the facts he brings forward. As yet it cannot be said
that the controversy has been brought to final settlement. Still, it is
hardly to be doubted that now, since the periodic law has seemed to
join hands with the spectroscope, a belief in the compound nature of the
so-called elements is rapidly gaining ground among chemists. More and
more general becomes the belief that the Daltonian atom is really a
compound radical, and that back of the seeming diversity of the alleged
elements is a single form of primordial matter. Indeed, in very recent
months, direct experimental evidence for this view has at last come to
hand, through the study of radio-active substances. In a later chapter
we shall have occasion to inquire how this came about.




IV. ANATOMY AND PHYSIOLOGY IN THE EIGHTEENTH CENTURY

ALBRECHT VON HALLER

An epoch in physiology was made in the eighteenth century by the genius
and efforts of Albrecht von Haller (1708-1777), of Berne, who is perhaps
as worthy of the title "The Great" as any philosopher who has been
so christened by his contemporaries since the time of Hippocrates.
Celebrated as a physician, he was proficient in various fields, being
equally famed in his own time as poet, botanist, and statesman, and
dividing his attention between art and science.

As a child Haller was so sickly that he was unable to amuse himself with
the sports and games common to boys of his age, and so passed most of
his time poring over books. When ten years of age he began writing poems
in Latin and German, and at fifteen entered the University of Tubingen.
At seventeen he wrote learned articles in opposition to certain accepted
doctrines, and at nineteen he received his degree of doctor. Soon after
this he visited England, where his zeal in dissecting brought him under
suspicion of grave-robbery, which suspicion made it expedient for him to
return to the Continent. After studying botany in Basel for some time he
made an extended botanical journey through Switzerland, finally settling
in his native city, Berne, as a practising physician. During this time
he did not neglect either poetry or botany, publishing anonymously a
collection of poems.

In 1736 he was called to Gottingen as professor of anatomy, surgery,
chemistry, and botany. During his labors in the university he never
neglected his literary work, sometimes living and sleeping for days and
nights together in his library, eating his meals while delving in his
books, and sleeping only when actually compelled to do so by fatigue.
During all this time he was in correspondence with savants from all over
the world, and it is said of him that he never left a letter of any kind
unanswered.

Haller's greatest contribution to medical science was his famous
doctrine of irritability, which has given him the name of "father of
modern nervous physiology," just as Harvey is called "the father of
the modern physiology of the blood." It has been said of this
famous doctrine of irritability that "it moved all the minds of the
century--and not in the departments of medicine alone--in a way of which
we of the present day have no satisfactory conception, unless we compare
it with our modern Darwinism."(1)

The principle of general irritability had been laid down by Francis
Glisson (1597-1677) from deductive studies, but Haller proved by
experiments along the line of inductive methods that this irritability
was not common to all "fibre as well as to the fluids of the body," but
something entirely special, and peculiar only to muscular substance. He
distinguished between irritability of muscles and sensibility of nerves.
In 1747 he gave as the three forces that produce muscular movements:
elasticity, or "dead nervous force"; irritability, or "innate nervous
force"; and nervous force in itself. And in 1752 he described one
hundred and ninety experiments for determining what parts of the body
possess "irritability"--that is, the property of contracting when
stimulated. His conclusion that this irritability exists in muscular
substance alone and is quite independent of the nerves proceeding to it
aroused a controversy that was never definitely settled until late in
the nineteenth century, when Haller's theory was found to be entirely
correct.

It was in pursuit of experiments to establish his theory of irritability
that Haller made his chief discoveries in embryology and development. He
proved that in the process of incubation of the egg the first trace of
the heart of the chick shows itself in the thirty-eighth hour, and that
the first trace of red blood showed in the forty-first hour. By his
investigations upon the lower animals he attempted to confirm the theory
that since the creation of genus every individual is derived from a
preceding individual--the existing theory of preformation, in which
he believed, and which taught that "every individual is fully and
completely preformed in the germ, simply growing from microscopic to
visible proportions, without developing any new parts."

In physiology, besides his studies of the nervous system, Haller studied
the mechanism of respiration, refuting the teachings of Hamberger
(1697-1755), who maintained that the lungs contract independently.
Haller, however, in common with his contemporaries, failed utterly to
understand the true function of the lungs. The great physiologist's
influence upon practical medicine, while most profound, was largely
indirect. He was a theoretical rather than a practical physician, yet he
is credited with being the first physician to use the watch in counting
the pulse.


BATTISTA MORGAGNI AND MORBID ANATOMY

A great contemporary of Haller was Giovanni Battista Morgagni
(1682-1771), who pursued what Sydenham had neglected, the investigation
in anatomy, thus supplying a necessary counterpart to the great
Englishman's work. Morgagni's investigations were directed chiefly to
the study of morbid anatomy--the study of the structure of diseased
tissue, both during life and post mortem, in contrast to the normal
anatomical structures. This work cannot be said to have originated
with him; for as early as 1679 Bonnet had made similar, although less
extensive, studies; and later many investigators, such as Lancisi and
Haller, had made post-mortem studies. But Morgagni's De sedibus et
causis morborum per anatomen indagatis was the largest, most accurate,
and best-illustrated collection of cases that had ever been brought
together, and marks an epoch in medical science. From the time of the
publication of Morgagni's researches, morbid anatomy became a recognized
branch of the medical science, and the effect of the impetus thus given
it has been steadily increasing since that time.


WILLIAM HUNTER

William Hunter (1718-1783) must always be remembered as one of the
greatest physicians and anatomists of the eighteenth century, and
particularly as the first great teacher of anatomy in England; but his
fame has been somewhat overshadowed by that of his younger brother John.

Hunter had been intended and educated for the Church, but on the advice
of the surgeon William Cullen he turned his attention to the study of
medicine. His first attempt at teaching was in 1746, when he delivered
a series of lectures on surgery for the Society of Naval Practitioners.
These lectures proved so interesting and instructive that he was at
once invited to give others, and his reputation as a lecturer was soon
established. He was a natural orator and story-teller, and he combined
with these attractive qualities that of thoroughness and clearness in
demonstrations, and although his lectures were two hours long he made
them so full of interest that his pupils seldom tired of listening.
He believed that he could do greater good to the world by "publicly
teaching his art than by practising it," and even during the last few
days of his life, when he was so weak that his friends remonstrated
against it, he continued his teaching, fainting from exhaustion at the
end of his last lecture, which preceded his death by only a few days.

For many years it was Hunter's ambition to establish a museum where the
study of anatomy, surgery, and medicine might be advanced, and in 1765
he asked for a grant of a plot of ground for this purpose, offering to
spend seven thousand pounds on its erection besides endowing it with a
professorship of anatomy. Not being able to obtain this grant, however,
he built a house, in which were lecture and dissecting rooms, and his
museum. In this museum were anatomical preparations, coins, minerals,
and natural-history specimens.

Hunter's weakness was his love of controversy and his resentment of
contradiction. This brought him into strained relations with many of
the leading physicians of his time, notably his own brother John, who
himself was probably not entirely free from blame in the matter. Hunter
is said to have excused his own irritability on the grounds that being
an anatomist, and accustomed to "the passive submission of dead bodies,"
contradictions became the more unbearable. Many of the physiological
researches begun by him were carried on and perfected by his more famous
brother, particularly his investigations of the capillaries, but he
added much to the anatomical knowledge of several structures of the
body, notably as to the structure of cartilages and joints.


JOHN HUNTER

In Abbot Islip's chapel in Westminster Abbey, close to the resting-place
of Ben Jonson, rest the remains of John Hunter (1728-1793), famous in
the annals of medicine as among the greatest physiologists and surgeons
that the world has ever produced: a man whose discoveries and inventions
are counted by scores, and whose field of research was only limited by
the outermost boundaries of eighteenth-century science, although his
efforts were directed chiefly along the lines of his profession.

Until about twenty years of age young Hunter had shown little aptitude
for study, being unusually fond of out-door sports and amusements; but
about that time, realizing that some occupation must be selected, he
asked permission of his brother William to attempt some dissections in
his anatomical school in London. To the surprise of his brother he made
this dissection unusually well; and being given a second, he acquitted
himself with such skill that his brother at once predicted that he would
become a great anatomist. Up to this time he had had no training of
any kind to prepare him for his professional career, and knew little of
Greek or Latin--languages entirely unnecessary for him, as he proved
in all of his life work. Ottley tells the story that, when twitted with
this lack of knowledge of the "dead languages" in after life, he said
of his opponent, "I could teach him that on the dead body which he never
knew in any language, dead or living."

By his second year in dissection he had become so skilful that he was
given charge of some of the classes in his brother's school; in 1754 he
became a surgeon's pupil in St. George's Hospital, and two years later
house-surgeon. Having by overwork brought on symptoms that seemed to
threaten consumption, he accepted the position of staff-surgeon to an
expedition to Belleisle in 1760, and two years later was serving with
the English army at Portugal. During all this time he was constantly
engaged in scientific researches, many of which, such as his
observations of gun-shot wounds, he put to excellent use in later life.
On returning to England much improved in health in 1763, he entered at
once upon his career as a London surgeon, and from that time forward
his progress was a practically uninterrupted series of successes in his
profession.

Hunter's work on the study of the lymphatics was of great service to
the medical profession. This important net-work of minute vessels
distributed throughout the body had recently been made the object of
much study, and various students, including Haller, had made extensive
investigations since their discovery by Asellius. But Hunter, in 1758,
was the first to discover the lymphatics in the neck of birds, although
it was his brother William who advanced the theory that the function
of these vessels was that of absorbents. One of John Hunter's pupils,
William Hewson (1739-1774), first gave an account, in 1768, of
the lymphatics in reptiles and fishes, and added to his teacher's
investigations of the lymphatics in birds. These studies of the
lymphatics have been regarded, perhaps with justice, as Hunter's most
valuable contributions to practical medicine.

In 1767 he met with an accident by which he suffered a rupture of
the tendo Achillis--the large tendon that forms the attachment of the
muscles of the calf to the heel. From observations of this accident,
and subsequent experiments upon dogs, he laid the foundation for the
now simple and effective operation for the cure of club feet and other
deformities involving the tendons. In 1772 he moved into his residence
at Earlscourt, Brompton, where he gathered about him a great menagerie
of animals, birds, reptiles, insects, and fishes, which he used in his
physiological and surgical experiments. Here he performed a countless
number of experiments--more, probably, than "any man engaged in
professional practice has ever conducted." These experiments varied
in nature from observations of the habits of bees and wasps to major
surgical operations performed upon hedgehogs, dogs, leopards, etc. It
is said that for fifteen years he kept a flock of geese for the sole
purpose of studying the process of development in eggs.

Hunter began his first course of lectures in 1772, being forced to do
this because he had been so repeatedly misquoted, and because he felt
that he could better gauge his own knowledge in this way. Lecturing was
a sore trial to him, as he was extremely diffident, and without writing
out his lectures in advance he was scarcely able to speak at all. In
this he presented a marked contrast to his brother William, who was
a fluent and brilliant speaker. Hunter's lectures were at best simple
readings of the facts as he had written them, the diffident teacher
seldom raising his eyes from his manuscript and rarely stopping
until his complete lecture had been read through. His lectures were,
therefore, instructive rather than interesting, as he used infinite care
in preparing them; but appearing before his classes was so dreaded by
him that he is said to have been in the habit of taking a half-drachm of
laudanum before each lecture to nerve him for the ordeal. One is led to
wonder by what name he shall designate that quality of mind that renders
a bold and fearless surgeon like Hunter, who is undaunted in the face
of hazardous and dangerous operations, a stumbling, halting, and
"frightened" speaker before a little band of, at most, thirty young
medical students. And yet this same thing is not unfrequently seen among
the boldest surgeons.


Hunter's Operation for the Cure of Aneurisms

It should be an object-lesson to those who, ignorantly or otherwise,
preach against the painless vivisection as practised to-day, that by the
sacrifice of a single deer in the cause of science Hunter discovered a
fact in physiology that has been the means of saving thousands of human
lives and thousands of human bodies from needless mutilation. We refer
to the discovery of the "collateral circulation" of the blood,
which led, among other things, to Hunter's successful operation upon
aneurisms.

Simply stated, every organ or muscle of the body is supplied by one
large artery, whose main trunk distributes the blood into its lesser
branches, and thence through the capillaries. Cutting off this main
artery, it would seem, should cut off entirely the blood-supply to the
particular organ which is supplied by this vessel; and until the time of
Hunter's demonstration this belief was held by most physiologists. But
nature has made a provision for this possible stoppage of blood-supply
from a single source, and has so arranged that some of the small
arterial branches coming from the main supply-trunk are connected with
other arterial branches coming from some other supply-trunk. Under
normal conditions the main arterial trunks supply their respective
organs, the little connecting arterioles playing an insignificant part.
But let the main supply-trunk be cut off or stopped for whatever reason,
and a remarkable thing takes place. The little connecting branches
begin at once to enlarge and draw blood from the neighboring uninjured
supply-trunk, This enlargement continues until at last a new route for
the circulation has been established, the organ no longer depending
on the now defunct original arterial trunk, but getting on as well as
before by this "collateral" circulation that has been established.

The thorough understanding of this collateral circulation is one of the
most important steps in surgery, for until it was discovered amputations
were thought necessary in such cases as those involving the artery
supplying a leg or arm, since it was supposed that, the artery being
stopped, death of the limb and the subsequent necessity for amputation
were sure to follow. Hunter solved this problem by a single operation
upon a deer, and his practicality as a surgeon led him soon after to
apply this knowledge to a certain class of surgical cases in a most
revolutionary and satisfactory manner.

What led to Hunter's far-reaching discovery was his investigation as to
the cause of the growth of the antlers of the deer. Wishing to ascertain
just what part the blood-supply on the opposite sides of the neck played
in the process of development, or, perhaps more correctly, to see what
effect cutting off the main blood-supply would have, Hunter had one of
the deer of Richmond Park caught and tied, while he placed a ligature
around one of the carotid arteries--one of the two principal arteries
that supply the head with blood. He observed that shortly after this the
antler (which was only half grown and consequently very vascular) on the
side of the obliterated artery became cold to the touch--from the lack
of warmth-giving blood. There was nothing unexpected in this, and Hunter
thought nothing of it until a few days later, when he found, to his
surprise, that the antler had become as warm as its fellow, and was
apparently increasing in size. Puzzled as to how this could be, and
suspecting that in some way his ligature around the artery had not been
effective, he ordered the deer killed, and on examination was astonished
to find that while his ligature had completely shut off the blood-supply
from the source of that carotid artery, the smaller arteries had become
enlarged so as to supply the antler with blood as well as ever, only by
a different route.

Hunter soon had a chance to make a practical application of the
knowledge thus acquired. This was a case of popliteal aneurism,
operations for which had heretofore proved pretty uniformly fatal. An
aneurism, as is generally understood, is an enlargement of a certain
part of an artery, this enlargement sometimes becoming of enormous size,
full of palpitating blood, and likely to rupture with fatal results at
any time. If by any means the blood can be allowed to remain quiet for
even a few hours in this aneurism it will form a clot, contract, and
finally be absorbed and disappear without any evil results. The problem
of keeping the blood quiet, with the heart continually driving it
through the vessel, is not a simple one, and in Hunter's time was
considered so insurmountable that some surgeons advocated amputation
of any member having an aneurism, while others cut down upon the tumor
itself and attempted to tie off the artery above and below. The first
of these operations maimed the patient for life, while the second was
likely to prove fatal.

In pondering over what he had learned about collateral circulation and
the time required for it to become fully established, Hunter conceived
the idea that if the blood-supply was cut off from above the aneurism,
thus temporarily preventing the ceaseless pulsations from the heart,
this blood would coagulate and form a clot before the collateral
circulation could become established or could affect it. The patient
upon whom he performed his now celebrated operation was afflicted with
a popliteal aneurism--that is, the aneurism was located on the large
popliteal artery just behind the knee-joint. Hunter, therefore, tied off
the femoral, or main supplying artery in the thigh, a little distance
above the aneurism. The operation was entirely successful, and in six
weeks' time the patient was able to leave the hospital, and with two
sound limbs. Naturally the simplicity and success of this operation
aroused the attention of Europe, and, alone, would have made the name of
Hunter immortal in the annals of surgery. The operation has ever since
been called the "Hunterian" operation for aneurism, but there is reason
to believe that Dominique Anel (born about 1679) performed a somewhat
similar operation several years earlier. It is probable, however, that
Hunter had never heard of this work of Anel, and that his operation
was the outcome of his own independent reasoning from the facts he had
learned about collateral circulation. Furthermore, Hunter's mode of
operation was a much better one than Anel's, and, while Anel's must
claim priority, the credit of making it widely known will always be
Hunter's.

The great services of Hunter were recognized both at home and abroad,
and honors and positions of honor and responsibility were given him. In
1776 he was appointed surgeon-extraordinary to the king; in 1783 he
was elected a member of the Royal Society of Medicine and of the Royal
Academy of Surgery at Paris; in 1786 he became deputy surgeon-general
of the army; and in 1790 he was appointed surgeon-general and
inspector-general of hospitals. All these positions he filled with
credit, and he was actively engaged in his tireless pursuit of knowledge
and in discharging his many duties when in October, 1793, he was
stricken while addressing some colleagues, and fell dead in the arms of
a fellow-physician.


LAZZARO SPALLANZANI

Hunter's great rival among contemporary physiologists was the Italian
Lazzaro Spallanzani (1729-1799), one of the most picturesque figures
in the history of science. He was not educated either as a scientist or
physician, devoting, himself at first to philosophy and the languages,
afterwards studying law, and later taking orders. But he was a keen
observer of nature and of a questioning and investigating mind, so that
he is remembered now chiefly for his discoveries and investigations
in the biological sciences. One important demonstration was his
controversion of the theory of abiogenesis, or "spontaneous generation,"
as propounded by Needham and Buffon. At the time of Needham's
experiments it had long been observed that when animal or vegetable
matter had lain in water for a little time--long enough for it to begin
to undergo decomposition--the water became filled with microscopic
creatures, the "infusoria animalculis." This would tend to show, either
that the water or the animal or vegetable substance contained the
"germs" of these minute organisms, or else that they were generated
spontaneously. It was known that boiling killed these animalcules,
and Needham agreed, therefore, that if he first heated the meat or
vegetables, and also the water containing them, and then placed them in
hermetically scaled jars--if he did this, and still the animalcules
made their appearance, it would be proof-positive that they had been
generated spontaneously. Accordingly he made numerous experiments,
always with the same results--that after a few days the water was found
to swarm with the microscopic creatures. The thing seemed proven beyond
question--providing, of course, that there had been no slips in the
experiments.

But Abbe Spallanzani thought that he detected such slips in Needham's
experiment. The possibility of such slips might come in several ways:
the contents of the jar might not have been boiled for a sufficient
length of time to kill all the germs, or the air might not have
been excluded completely by the sealing process. To cover both these
contingencies, Spallanzani first hermetically sealed the glass vessels
and then boiled them for three-quarters of an hour. Under these
circumstances no animalcules ever made their appearance--a conclusive
demonstration that rendered Needham's grounds for his theory at once
untenable.(2)

Allied to these studies of spontaneous generation were Spallanzani's
experiments and observations on the physiological processes of
generation among higher animals. He experimented with frogs, tortoises,
and dogs; and settled beyond question the function of the ovum and
spermatozoon. Unfortunately he misinterpreted the part played by the
spermatozoa in believing that their surrounding fluid was equally active
in the fertilizing process, and it was not until some forty years later
(1824) that Dumas corrected this error.


THE CHEMICAL THEORY OF DIGESTION

Among the most interesting researches of Spallanzani were his
experiments to prove that digestion, as carried on in the stomach, is a
chemical process. In this he demonstrated, as Rene Reaumur had attempted
to demonstrate, that digestion could be carried on outside the walls of
the stomach as an ordinary chemical reaction, using the gastric juice
as the reagent for performing the experiment. The question as to whether
the stomach acted as a grinding or triturating organ, rather than as a
receptacle for chemical action, had been settled by Reaumur and was
no longer a question of general dispute. Reaumur had demonstrated
conclusively that digestion would take place in the stomach in the same
manner and the same time if the substance to be digested was protected
from the peristalic movements of the stomach and subjected to the action
of the gastric juice only. He did this by introducing the substances to
be digested into the stomach in tubes, and thus protected so that while
the juices of the stomach could act upon them freely they would not be
affected by any movements of the organ.

Following up these experiments, he attempted to show that digestion
could take place outside the body as well as in it, as it certainly
should if it were a purely chemical process. He collected quantities
of gastric juice, and placing it in suitable vessels containing crushed
grain or flesh, kept the mixture at about the temperature of the body
for several hours. After repeated experiments of this kind, apparently
conducted with great care, Reaumur reached the conclusion that "the
gastric juice has no more effect out of the living body in dissolving
or digesting the food than water, mucilage, milk, or any other bland
fluid."(3) Just why all of these experiments failed to demonstrate a
fact so simple does not appear; but to Spallanzani, at least, they
were by no means conclusive, and he proceeded to elaborate upon the
experiments of Reaumur. He made his experiments in scaled tubes exposed
to a certain degree of heat, and showed conclusively that the chemical
process does go on, even when the food and gastric juice are removed
from their natural environment in the stomach. In this he was opposed
by many physiologists, among them John Hunter, but the truth of his
demonstrations could not be shaken, and in later years we find Hunter
himself completing Spallanzani's experiments by his studies of the
post-mortem action of the gastric juice upon the stomach walls.

That Spallanzani's and Hunter's theories of the action of the gastric
juice were not at once universally accepted is shown by an essay written
by a learned physician in 1834. In speaking of some of Spallanzani's
demonstrations, he writes: "In some of the experiments, in order to give
the flesh or grains steeped in the gastric juice the same temperature
with the body, the phials were introduced under the armpits. But this is
not a fair mode of ascertaining the effects of the gastric juice out of
the body; for the influence which life may be supposed to have on the
solution of the food would be secured in this case. The affinities
connected with life would extend to substances in contact with any part
of the system: substances placed under the armpits are not placed at
least in the same circumstances with those unconnected with a living
animal." But just how this writer reaches the conclusion that "the
experiments of Reaumur and Spallanzani give no evidence that the gastric
juice has any peculiar influence more than water or any other bland
fluid in digesting the food"(4) is difficult to understand.

The concluding touches were given to the new theory of digestion by
John Hunter, who, as we have seen, at first opposed Spallanzani, but
who finally became an ardent champion of the chemical theory. Hunter now
carried Spallanzani's experiments further and proved the action of the
digestive fluids after death. For many years anatomists had been puzzled
by pathological lesion of the stomach, found post mortem, when no
symptoms of any disorder of the stomach had been evinced during life.
Hunter rightly conceived that these lesions were caused by the action
of the gastric juice, which, while unable to act upon the living tissue,
continued its action chemically after death, thus digesting the walls
of the stomach in which it had been formed. And, as usual with his
observations, he turned this discovery to practical use in accounting
for certain phenomena of digestion. The following account of the stomach
being digested after death was written by Hunter at the desire of
Sir John Pringle, when he was president of the Royal Society, and the
circumstance which led to this is as follows: "I was opening, in his
presence, the body of a patient of his own, where the stomach was in
part dissolved, which appeared to him very unaccountable, as there had
been no previous symptom that could have led him to suspect any
disease in the stomach. I took that opportunity of giving him my ideas
respecting it, and told him that I had long been making experiments
on digestion, and considered this as one of the facts which proved a
converting power in the gastric juice.... There are a great many powers
in nature which the living principle does not enable the animal matter,
with which it is combined, to resist--viz., the mechanical and most
of the strongest chemical solvents. It renders it, however, capable of
resisting the powers of fermentation, digestion, and perhaps several
others, which are well known to act on the same matter when deprived of
the living principle and entirely to decompose it."

Hunter concludes his paper with the following paragraph: "These
appearances throw considerable light on the principle of digestion,
and show that it is neither a mechanical power, nor contractions of the
stomach, nor heat, but something secreted in the coats of the stomach,
and thrown into its cavity, which there animalizes the food or
assimilates it to the nature of the blood. The power of this juice is
confined or limited to certain substances, especially of the vegetable
and animal kingdoms; and although this menstruum is capable of acting
independently of the stomach, yet it is indebted to that viscus for its
continuance."(5)


THE FUNCTION OF RESPIRATION

It is a curious commentary on the crude notions of mechanics of previous
generations that it should have been necessary to prove by experiment
that the thin, almost membranous stomach of a mammal has not the power
to pulverize, by mere attrition, the foods that are taken into it.
However, the proof was now for the first time forthcoming, and the
question of the general character of the function of digestion was
forever set at rest. Almost simultaneously with this great advance,
corresponding progress was made in an allied field: the mysteries of
respiration were at last cleared up, thanks to the new knowledge of
chemistry. The solution of the problem followed almost as a matter
of course upon the advances of that science in the latter part of the
century. Hitherto no one since Mayow, of the previous century, whose
flash of insight had been strangely overlooked and forgotten, had even
vaguely surmised the true function of the lungs. The great Boerhaave
had supposed that respiration is chiefly important as an aid to the
circulation of the blood; his great pupil, Haller, had believed to the
day of his death in 1777 that the main purpose of the function is to
form the voice. No genius could hope to fathom the mystery of the lungs
so long as air was supposed to be a simple element, serving a mere
mechanical purpose in the economy of the earth.

But the discovery of oxygen gave the clew, and very soon all the
chemists were testing the air that came from the lungs--Dr. Priestley,
as usual, being in the van. His initial experiments were made in
1777, and from the outset the problem was as good as solved. Other
experimenters confirmed his results in all their essentials--notably
Scheele and Lavoisier and Spallanzani and Davy. It was clearly
established that there is chemical action in the contact of the air with
the tissue of the lungs; that some of the oxygen of the air disappears,
and that carbonic-acid gas is added to the inspired air. It was shown,
too, that the blood, having come in contact with the air, is changed
from black to red in color. These essentials were not in dispute from
the first. But as to just what chemical changes caused these results
was the subject of controversy. Whether, for example, oxygen is actually
absorbed into the blood, or whether it merely unites with carbon given
off from the blood, was long in dispute.

Each of the main disputants was biased by his own particular views as
to the moot points of chemistry. Lavoisier, for example, believed oxygen
gas to be composed of a metal oxygen combined with the alleged element
heat; Dr. Priestley thought it a compound of positive electricity and
phlogiston; and Humphry Davy, when he entered the lists a little later,
supposed it to be a compound of oxygen and light. Such mistaken notions
naturally complicated matters and delayed a complete understanding of
the chemical processes of respiration. It was some time, too, before the
idea gained acceptance that the most important chemical changes do not
occur in the lungs themselves, but in the ultimate tissues. Indeed,
the matter was not clearly settled at the close of the century.
Nevertheless, the problem of respiration had been solved in its
essentials. Moreover, the vastly important fact had been established
that a process essentially identical with respiration is necessary to
the existence not only of all creatures supplied with lungs, but to
fishes, insects, and even vegetables--in short, to every kind of living
organism.


ERASMUS DARWIN AND VEGETABLE PHYSIOLOGY

Some interesting experiments regarding vegetable respiration were made
just at the close of the century by Erasmus Darwin, and recorded in his
Botanic Garden as a foot-note to the verse:

"While spread in air the leaves respiring play."


These notes are worth quoting at some length, as they give a clear idea
of the physiological doctrines of the time (1799), while taking advance
ground as to the specific matter in question:


"There have been various opinions," Darwin says, "concerning the use of
the leaves of plants in the vegetable economy. Some have contended
that they are perspiratory organs. This does not seem probable from an
experiment of Dr. Hales, Vegetable Statics, p. 30. He, found, by cutting
off branches of trees with apples on them and taking off the leaves,
that an apple exhaled about as much as two leaves the surfaces of which
were nearly equal to the apple; whence it would appear that apples have
as good a claim to be termed perspiratory organs as leaves. Others have
believed them excretory organs of excrementitious juices, but as
the vapor exhaled from vegetables has no taste, this idea is no more
probable than the other; add to this that in most weathers they do not
appear to perspire or exhale at all.

"The internal surface of the lungs or air-vessels in men is said to
be equal to the external surface of the whole body, or almost fifteen
square feet; on this surface the blood is exposed to the influence of
the respired air through the medium, however, of a thin pellicle; by
this exposure to the air it has its color changed from deep red to
bright scarlet, and acquires something so necessary to the existence of
life that we can live scarcely a minute without this wonderful process.

"The analogy between the leaves of plants and the lungs or gills of
animals seems to embrace so many circumstances that we can scarcely
withhold our consent to their performing similar offices.

"1. The great surface of leaves compared to that of the trunk and
branches of trees is such that it would seem to be an organ well adapted
for the purpose of exposing the vegetable juices to the influence of the
air; this, however, we shall see afterwards is probably performed only
by their upper surfaces, yet even in this case the surface of the leaves
in general bear a greater proportion to the surface of the tree than the
lungs of animals to their external surfaces.

"2. In the lung of animals the blood, after having been exposed to the
air in the extremities of the pulmonary artery, is changed in color
from deep red to bright scarlet, and certainly in some of its essential
properties it is then collected by the pulmonary vein and returned
to the heart. To show a similarity of circumstances in the leaves of
plants, the following experiment was made, June 24, 1781. A stalk with
leaves and seed-vessels of large spurge (Euphorbia helioscopia) had been
several days placed in a decoction of madder (Rubia tinctorum) so that
the lower part of the stem and two of the undermost leaves were immersed
in it. After having washed the immersed leaves in clear water I could
readily discover the color of the madder passing along the middle rib
of each leaf. The red artery was beautifully visible on the under and on
the upper surface of the leaf; but on the upper side many red branches
were seen going from it to the extremities of the leaf, which on the
other side were not visible except by looking through it against the
light. On this under side a system of branching vessels carrying a
pale milky fluid were seen coming from the extremities of the leaf, and
covering the whole under side of it, and joining two large veins, one
on each side of the red artery in the middle rib of the leaf, and along
with it descending to the foot-stalk or petiole. On slitting one of
these leaves with scissors, and having a magnifying-glass ready, the
milky blood was seen oozing out of the returning veins on each side of
the red artery in the middle rib, but none of the red fluid from the
artery.

"All these appearances were more easily seen in a leaf of Picris treated
in the same manner; for in this milky plant the stems and middle rib of
the leaves are sometimes naturally colored reddish, and hence the color
of the madder seemed to pass farther into the ramifications of their
leaf-arteries, and was there beautifully visible with the returning
branches of milky veins on each side."


Darwin now goes on to draw an incorrect inference from his observations:


"3. From these experiments," he says, "the upper surface of the leaf
appeared to be the immediate organ of respiration, because the colored
fluid was carried to the extremities of the leaf by vessels most
conspicuous on the upper surface, and there changed into a milky fluid,
which is the blood of the plant, and then returned by concomitant
veins on the under surface, which were seen to ooze when divided with
scissors, and which, in Picris, particularly, render the under surface
of the leaves greatly whiter than the upper one."


But in point of fact, as studies of a later generation were to show, it
is the under surface of the leaf that is most abundantly provided
with stomata, or "breathing-pores." From the stand-point of this later
knowledge, it is of interest to follow our author a little farther,
to illustrate yet more fully the possibility of combining correct
observations with a faulty inference.


"4. As the upper surface of leaves constitutes the organ of respiration,
on which the sap is exposed in the termination of arteries beneath a
thin pellicle to the action of the atmosphere, these surfaces in many
plants strongly repel moisture, as cabbage leaves, whence the particles
of rain lying over their surfaces without touching them, as observed by
Mr. Melville (Essays Literary and Philosophical: Edinburgh), have the
appearance of globules of quicksilver. And hence leaves with the upper
surfaces on water wither as soon as in the dry air, but continue green
for many days if placed with the under surface on water, as appears
in the experiments of Monsieur Bonnet (Usage des Feuilles). Hence some
aquatic plants, as the water-lily (Nymphoea), have the lower sides
floating on the water, while the upper surfaces remain dry in the air.

"5. As those insects which have many spiracula, or breathing apertures,
as wasps and flies, are immediately suffocated by pouring oil upon them,
I carefully covered with oil the surfaces of several leaves of phlomis,
of Portugal laurel, and balsams, and though it would not regularly
adhere, I found them all die in a day or two.

"It must be added that many leaves are furnished with muscles about
their foot-stalks, to turn their surfaces to the air or light, as mimosa
or Hedysarum gyrans. From all these analogies I think there can be no
doubt but that leaves of trees are their lungs, giving out a phlogistic
material to the atmosphere, and absorbing oxygen, or vital air.

"6. The great use of light to vegetation would appear from this theory
to be by disengaging vital air from the water which they perspire, and
thence to facilitate its union with their blood exposed beneath the
thin surface of their leaves; since when pure air is thus applied it
is probable that it can be more readily absorbed. Hence, in the curious
experiments of Dr. Priestley and Mr. Ingenhouz, some plants purified
less air than others--that is, they perspired less in the sunshine;
and Mr. Scheele found that by putting peas into water which about
half covered them they converted the vital air into fixed air, or
carbonic-acid gas, in the same manner as in animal respiration.

"7. The circulation in the lungs or leaves of plants is very similar
to that of fish. In fish the blood, after having passed through their
gills, does not return to the heart as from the lungs of air-breathing
animals, but the pulmonary vein taking the structure of an artery after
having received the blood from the gills, which there gains a more
florid color, distributes it to the other parts of their bodies. The
same structure occurs in the livers of fish, whence we see in those
animals two circulations independent of the power of the heart--viz.,
that beginning at the termination of the veins of the gills and
branching through the muscles, and that which passes through the liver;
both which are carried on by the action of those respective arteries and
veins."(6)

Darwin is here a trifle fanciful in forcing the analogy between plants
and animals. The circulatory system of plants is really not quite
so elaborately comparable to that of fishes as he supposed. But the
all-important idea of the uniformity underlying the seeming diversity
of Nature is here exemplified, as elsewhere in the writings of Erasmus
Darwin; and, more specifically, a clear grasp of the essentials of the
function of respiration is fully demonstrated.


ZOOLOGY AT THE CLOSE OF THE EIGHTEENTH CENTURY


Several causes conspired to make exploration all the fashion during the
closing epoch of the eighteenth century. New aid to the navigator
had been furnished by the perfected compass and quadrant, and by the
invention of the chronometer; medical science had banished scurvy, which
hitherto had been a perpetual menace to the voyager; and, above all, the
restless spirit of the age impelled the venturesome to seek novelty in
fields altogether new. Some started for the pole, others tried for a
northeast or northwest passage to India, yet others sought the great
fictitious antarctic continent told of by tradition. All these of course
failed of their immediate purpose, but they added much to the world's
store of knowledge and its fund of travellers' tales.

Among all these tales none was more remarkable than those which told of
strange living creatures found in antipodal lands. And here, as did not
happen in every field, the narratives were often substantiated by the
exhibition of specimens that admitted no question. Many a company of
explorers returned more or less laden with such trophies from the
animal and vegetable kingdoms, to the mingled astonishment, delight, and
bewilderment of the closet naturalists. The followers of Linnaeus in the
"golden age of natural history," a few decades before, had increased the
number of known species of fishes to about four hundred, of birds to one
thousand, of insects to three thousand, and of plants to ten thousand.
But now these sudden accessions from new territories doubled the figure
for plants, tripled it for fish and birds, and brought the number of
described insects above twenty thousand. Naturally enough, this wealth
of new material was sorely puzzling to the classifiers. The more
discerning began to see that the artificial system of Linnaeus,
wonderful and useful as it had been, must be advanced upon before the
new material could be satisfactorily disposed of. The way to a more
natural system, based on less arbitrary signs, had been pointed out by
Jussieu in botany, but the zoologists were not prepared to make headway
towards such a system until they should gain a wider understanding of
the organisms with which they had to deal through comprehensive studies
of anatomy. Such studies of individual forms in their relations to the
entire scale of organic beings were pursued in these last decades of
the century, but though two or three most important generalizations were
achieved (notably Kaspar Wolff's conception of the cell as the basis of
organic life, and Goethe's all-important doctrine of metamorphosis of
parts), yet, as a whole, the work of the anatomists of the period was
germinative rather than fruit-bearing. Bichat's volumes, telling of the
recognition of the fundamental tissues of the body, did not begin to
appear till the last year of the century. The announcement by Cuvier of
the doctrine of correlation of parts bears the same date, but in general
the studies of this great naturalist, which in due time were to stamp
him as the successor of Linnaeus, were as yet only fairly begun.




V. ANATOMY AND PHYSIOLOGY IN THE NINETEENTH CENTURY

CUVIER AND THE CORRELATION OF PARTS

We have seen that the focal points of the physiological world towards
the close of the eighteenth century were Italy and England, but when
Spallanzani and Hunter passed away the scene shifted to France. The
time was peculiarly propitious, as the recent advances in many lines of
science had brought fresh data for the student of animal life which were
in need of classification, and, as several minds capable of such a task
were in the field, it was natural that great generalizations should have
come to be quite the fashion. Thus it was that Cuvier came forward with
a brand-new classification of the animal kingdom, establishing
four great types of being, which he called vertebrates, mollusks,
articulates, and radiates. Lamarck had shortly before established the
broad distinction between animals with and those without a backbone;
Cuvier's Classification divided the latter--the invertebrates--into
three minor groups. And this division, familiar ever since to all
students of zoology, has only in very recent years been supplanted, and
then not by revolution, but by a further division, which the elaborate
recent studies of lower forms of life seemed to make desirable.

In the course of those studies of comparative anatomy which led to his
new classification, Cuvier's attention was called constantly to the
peculiar co-ordination of parts in each individual organism. Thus an
animal with sharp talons for catching living prey--as a member of the
cat tribe--has also sharp teeth, adapted for tearing up the flesh of its
victim, and a particular type of stomach, quite different from that of
herbivorous creatures. This adaptation of all the parts of the animal
to one another extends to the most diverse parts of the organism, and
enables the skilled anatomist, from the observation of a single typical
part, to draw inferences as to the structure of the entire animal--a
fact which was of vast aid to Cuvier in his studies of paleontology. It
did not enable Cuvier, nor does it enable any one else, to reconstruct
fully the extinct animal from observation of a single bone, as has
sometimes been asserted, but what it really does establish, in the hands
of an expert, is sufficiently astonishing.

"While the study of the fossil remains of the greater quadrupeds is more
satisfactory," he writes, "by the clear results which it affords, than
that of the remains of other animals found in a fossil state, it is also
complicated with greater and more numerous difficulties. Fossil shells
are usually found quite entire, and retaining all the characters
requisite for comparing them with the specimens contained in collections
of natural history, or represented in the works of naturalists. Even the
skeletons of fishes are found more or less entire, so that the general
forms of their bodies can, for the most part, be ascertained,
and usually, at least, their generic and specific characters are
determinable, as these are mostly drawn from their solid parts. In
quadrupeds, on the contrary, even when their entire skeletons are
found, there is great difficulty in discovering their distinguishing
characters, as these are chiefly founded upon their hairs and colors and
other marks which have disappeared previous to their incrustation. It is
also very rare to find any fossil skeletons of quadrupeds in any degree
approaching to a complete state, as the strata for the most part only
contain separate bones, scattered confusedly and almost always broken
and reduced to fragments, which are the only means left to naturalists
for ascertaining the species or genera to which they have belonged.

"Fortunately comparative anatomy, when thoroughly understood, enables
us to surmount all these difficulties, as a careful application of its
principles instructs us in the correspondences and dissimilarities of
the forms of organized bodies of different kinds, by which each may be
rigorously ascertained from almost every fragment of its various parts
and organs.

"Every organized individual forms an entire system of its own, all the
parts of which naturally correspond, and concur to produce a certain
definite purpose, by reciprocal reaction, or by combining towards the
same end. Hence none of these separate parts can change their forms
without a corresponding change in the other parts of the same animal,
and consequently each of these parts, taken separately, indicates all
the other parts to which it has belonged. Thus, as I have elsewhere
shown, if the viscera of an animal are so organized as only to be fitted
for the digestion of recent flesh, it is also requisite that the jaws
should be so constructed as to fit them for devouring prey; the claws
must be constructed for seizing and tearing it to pieces; the teeth
for cutting and dividing its flesh; the entire system of the limbs,
or organs of motion, for pursuing and overtaking it; and the organs of
sense for discovering it at a distance. Nature must also have endowed
the brain of the animal with instincts sufficient for concealing itself
and for laying plans to catch its necessary victims....

"To enable the animal to carry off its prey when seized, a corresponding
force is requisite in the muscles which elevate the head, and this
necessarily gives rise to a determinate form of the vertebrae to which
these muscles are attached and of the occiput into which they are
inserted. In order that the teeth of a carnivorous animal may be able to
cut the flesh, they require to be sharp, more or less so in proportion
to the greater or less quantity of flesh that they have to cut. It is
requisite that their roots should be solid and strong, in proportion to
the quantity and size of the bones which they have to break to pieces.
The whole of these circumstances must necessarily influence the
development and form of all the parts which contribute to move the
jaws...."

After these observations, it will be easily seen that similar
conclusions may be drawn with respect to the limbs of carnivorous
animals, which require particular conformations to fit them for rapidity
of motion in general; and that similar considerations must influence the
forms and connections of the vertebrae and other bones constituting the
trunk of the body, to fit them for flexibility and readiness of motion
in all directions. The bones also of the nose, of the orbit, and of
the ears require certain forms and structures to fit them for giving
perfection to the senses of smell, sight, and hearing, so necessary to
animals of prey. In short, the shape and structure of the teeth regulate
the forms of the condyle, of the shoulder-blade, and of the claws,
in the same manner as the equation of a curve regulates all its other
properties; and as in regard to any particular curve all its properties
may be ascertained by assuming each separate property as the foundation
of a particular equation, in the same manner a claw, a shoulder-blade,
a condyle, a leg or arm bone, or any other bone separately considered,
enables us to discover the description of teeth to which they have
belonged; and so also reciprocally we may determine the forms of the
other bones from the teeth. Thus commencing our investigations by a
careful survey of any one bone by itself, a person who is sufficiently
master of the laws of organic structure may, as it were, reconstruct the
whole animal to which that bone belonged."(1)

We have already pointed out that no one is quite able to perform the
necromantic feat suggested in the last sentence; but the exaggeration is
pardonable in the enthusiast to whom the principle meant so much and in
whose hands it extended so far.

Of course this entire principle, in its broad outlines, is something
with which every student of anatomy had been familiar from the time
when anatomy was first studied, but the full expression of the "law
of co-ordination," as Cuvier called it, had never been explicitly made
before; and, notwithstanding its seeming obviousness, the exposition
which Cuvier made of it in the introduction to his classical work on
comparative anatomy, which was published during the first decade of
the nineteenth century, ranks as a great discovery. It is one of those
generalizations which serve as guideposts to other discoveries.


BICHAT AND THE BODILY TISSUES

Much the same thing may be said of another generalization regarding the
animal body, which the brilliant young French physician Marie Francois
Bichat made in calling attention to the fact that each vertebrate
organism, including man, has really two quite different sets of
organs--one set under volitional control, and serving the end of
locomotion, the other removed from volitional control, and serving the
ends of the "vital processes" of digestion, assimilation, and the like.
He called these sets of organs the animal system and the organic system,
respectively. The division thus pointed out was not quite new, for
Grimaud, professor of physiology in the University of Montpellier,
had earlier made what was substantially the same classification of the
functions into "internal or digestive and external or locomotive"; but
it was Bichat's exposition that gave currency to the idea.

Far more important, however, was another classification which Bichat put
forward in his work on anatomy, published just at the beginning of the
last century. This was the division of all animal structures into what
Bichat called tissues, and the pointing out that there are really only
a few kinds of these in the body, making up all the diverse organs. Thus
muscular organs form one system; membranous organs another; glandular
organs a third; the vascular mechanism a fourth, and so on. The
distinction is so obvious that it seems rather difficult to conceive
that it could have been overlooked by the earliest anatomists; but, in
point of fact, it is only obvious because now it has been familiarly
taught for almost a century. It had never been given explicit expression
before the time of Bichat, though it is said that Bichat himself was
somewhat indebted for it to his master, Desault, and to the famous
alienist Pinel.

However that may be, it is certain that all subsequent anatomists have
found Bichat's classification of the tissues of the utmost value in
their studies of the animal functions. Subsequent advances were to
show that the distinction between the various tissues is not really
so fundamental as Bichat supposed, but that takes nothing from the
practical value of the famous classification.

It was but a step from this scientific classification of tissues to a
similar classification of the diseases affecting them, and this was one
of the greatest steps towards placing medicine on the plane of an exact
science. This subject of these branches completely fascinated Bichat,
and he exclaimed, enthusiastically: "Take away some fevers and nervous
trouble, and all else belongs to the kingdom of pathological anatomy."
But out of this enthusiasm came great results. Bichat practised as he
preached, and, believing that it was only possible to understand disease
by observing the symptoms carefully at the bedside, and, if the disease
terminated fatally, by post-mortem examination, he was so arduous in his
pursuit of knowledge that within a period of less than six months he had
made over six hundred autopsies--a record that has seldom, if ever,
been equalled. Nor were his efforts fruitless, as a single example will
suffice to show. By his examinations he was able to prove that diseases
of the chest, which had formerly been classed under the indefinite name
"peripneumonia," might involve three different structures, the pleural
sac covering the lungs, the lung itself, and the bronchial tubes, the
diseases affecting these organs being known respectively as pleuritis,
pneumonia, and bronchitis, each one differing from the others as to
prognosis and treatment. The advantage of such an exact classification
needs no demonstration.


LISTER AND THE PERFECTED MICROSCOPE

At the same time when these broad macroscopical distinctions were being
drawn there were other workers who were striving to go even deeper into
the intricacies of the animal mechanism with the aid of the microscope.
This undertaking, however, was beset with very great optical
difficulties, and for a long time little advance was made upon the work
of preceding generations. Two great optical barriers, known technically
as spherical and chromatic aberration--the one due to a failure of the
rays of light to fall all in one plane when focalized through a lens,
the other due to the dispersive action of the lens in breaking the
white light into prismatic colors--confronted the makers of microscopic
lenses, and seemed all but insuperable. The making of achromatic lenses
for telescopes had been accomplished, it is true, by Dolland in the
previous century, by the union of lenses of crown glass with those of
flint glass, these two materials having different indices of refraction
and dispersion. But, aside from the mechanical difficulties which arise
when the lens is of the minute dimensions required for use with the
microscope, other perplexities are introduced by the fact that the use
of a wide pencil of light is a desideratum, in order to gain sufficient
illumination when large magnification is to be secured.

In the attempt to overcome those difficulties, the foremost physical
philosophers of the time came to the aid of the best opticians. Very
early in the century, Dr. (afterwards Sir David) Brewster, the renowned
Scotch physicist, suggested that certain advantages might accrue from
the use of such gems as have high refractive and low dispersive indices,
in place of lenses made of glass. Accordingly lenses were made of
diamond, of sapphire, and so on, and with some measure of success. But
in 1812 a much more important innovation was introduced by Dr. William
Hyde Wollaston, one of the greatest and most versatile, and, since
the death of Cavendish, by far the most eccentric of English natural
philosophers. This was the suggestion to use two plano-convex
lenses, placed at a prescribed distance apart, in lieu of the single
double-convex lens generally used. This combination largely overcame
the spherical aberration, and it gained immediate fame as the "Wollaston
doublet."

To obviate loss of light in such a doublet from increase of reflecting
surfaces, Dr. Brewster suggested filling the interspace between the two
lenses with a cement having the same index of refraction as the lenses
themselves--an improvement of manifest advantage. An improvement yet
more important was made by Dr. Wollaston himself in the introduction of
the diaphragm to limit the field of vision between the lenses, instead
of in front of the anterior lens. A pair of lenses thus equipped Dr.
Wollaston called the periscopic microscope. Dr. Brewster suggested that
in such a lens the same object might be attained with greater ease by
grinding an equatorial groove about a thick or globular lens and filling
the groove with an opaque cement. This arrangement found much favor,
and came subsequently to be known as a Coddington lens, though Mr.
Coddington laid no claim to being its inventor.

Sir John Herschel, another of the very great physicists of the time,
also gave attention to the problem of improving the microscope, and in
1821 he introduced what was called an aplanatic combination of lenses,
in which, as the name implies, the spherical aberration was largely
done away with. It was thought that the use of this Herschel aplanatic
combination as an eyepiece, combined with the Wollaston doublet for the
objective, came as near perfection as the compound microscope was likely
soon to come. But in reality the instrument thus constructed, though
doubtless superior to any predecessor, was so defective that for
practical purposes the simple microscope, such as the doublet or the
Coddington, was preferable to the more complicated one.

Many opticians, indeed, quite despaired of ever being able to make a
satisfactory refracting compound microscope, and some of them had taken
up anew Sir Isaac Newton's suggestion in reference to a reflecting
microscope. In particular, Professor Giovanni Battista Amici, a very
famous mathematician and practical optician of Modena, succeeded in
constructing a reflecting microscope which was said to be superior to
any compound microscope of the time, though the events of the ensuing
years were destined to rob it of all but historical value. For there
were others, fortunately, who did not despair of the possibilities of
the refracting microscope, and their efforts were destined before
long to be crowned with a degree of success not even dreamed of by any
preceding generation.

The man to whom chief credit is due for directing those final steps
that made the compound microscope a practical implement instead of a
scientific toy was the English amateur optician Joseph Jackson Lister.
Combining mathematical knowledge with mechanical ingenuity, and having
the practical aid of the celebrated optician Tulley, he devised formulae
for the combination of lenses of crown glass with others of flint
glass, so adjusted that the refractive errors of one were corrected
or compensated by the other, with the result of producing lenses of
hitherto unequalled powers of definition; lenses capable of showing an
image highly magnified, yet relatively free from those distortions
and fringes of color that had heretofore been so disastrous to true
interpretation of magnified structures.

Lister had begun his studies of the lens in 1824, but it was not until
1830 that he contributed to the Royal Society the famous paper detailing
his theories and experiments. Soon after this various continental
opticians who had long been working along similar lines took the matter
up, and their expositions, in particular that of Amici, introduced
the improved compound microscope to the attention of microscopists
everywhere. And it required but the most casual trial to convince the
experienced observers that a new implement of scientific research had
been placed in their hands which carried them a long step nearer
the observation of the intimate physical processes which lie at the
foundation of vital phenomena. For the physiologist this perfection of
the compound microscope had the same significance that the, discovery
of America had for the fifteenth-century geographers--it promised a
veritable world of utterly novel revelations. Nor was the fulfilment of
that promise long delayed.

Indeed, so numerous and so important were the discoveries now made in
the realm of minute anatomy that the rise of histology to the rank of an
independent science may be said to date from this period. Hitherto, ever
since the discovery of magnifying-glasses, there had been here and there
a man, such as Leuwenhoek or Malpighi, gifted with exceptional vision,
and perhaps unusually happy in his conjectures, who made important
contributions to the knowledge of the minute structure of organic
tissues; but now of a sudden it became possible for the veriest tyro to
confirm or refute the laborious observations of these pioneers, while
the skilled observer could step easily beyond the barriers of vision
that hitherto were quite impassable. And so, naturally enough, the
physiologists of the fourth decade of the nineteenth century rushed
as eagerly into the new realm of the microscope as, for example, their
successors of to-day are exploring the realm of the X-ray.

Lister himself, who had become an eager interrogator of the instrument
he had perfected, made many important discoveries, the most notable
being his final settlement of the long-mooted question as to the true
form of the red corpuscles of the human blood. In reality, as everybody
knows nowadays, these are biconcave disks, but owing to their peculiar
figure it is easily possible to misinterpret the appearances they
present when seen through a poor lens, and though Dr. Thomas Young and
various other observers had come very near the truth regarding them,
unanimity of opinion was possible only after the verdict of the
perfected microscope was given.

These blood corpuscles are so infinitesimal in size that something like
five millions of them are found in each cubic millimetre of the blood,
yet they are isolated particles, each having, so to speak, its own
personality. This, of course, had been known to microscopists since the
days of the earliest lenses. It had been noticed, too, by here and
there an observer, that certain of the solid tissues seemed to present
something of a granular texture, as if they, too, in their ultimate
constitution, were made up of particles. And now, as better and better
lenses were constructed, this idea gained ground constantly, though
for a time no one saw its full significance. In the case of vegetable
tissues, indeed, the fact that little particles encased a membranous
covering, and called cells, are the ultimate visible units of structure
had long been known. But it was supposed that animal tissues differed
radically from this construction. The elementary particles of vegetables
"were regarded to a certain extent as individuals which composed the
entire plant, while, on the other hand, no such view was taken of the
elementary parts of animals."


ROBERT BROWN AND THE CELL NUCLEUS

In the year 1833 a further insight into the nature of the ultimate
particles of plants was gained through the observation of the English
microscopist Robert Brown, who, in the course of his microscopic studies
of the epidermis of orchids, discovered in the cells "an opaque spot,"
which he named the nucleus. Doubtless the same "spot" had been seen
often enough before by other observers, but Brown was the first to
recognize it as a component part of the vegetable cell and to give it a
name.


"I shall conclude my observations on Orchideae," said Brown, "with a
notice of some points of their general structure, which chiefly relate
to the cellular tissue. In each cell of the epidermis of a great part
of this family, especially of those with membranous leaves, a single
circular areola, generally somewhat more opaque than, the membrane of
the cell, is observable. This areola, which is more or less distinctly
granular, is slightly convex, and although it seems to be on the surface
is in reality covered by the outer lamina of the cell. There is no
regularity as to its place in the cell; it is not unfrequently, however,
central or nearly so.

"As only one areola belongs to each cell, and as in many cases where it
exists in the common cells of the epidermis, it is also visible in the
cutaneous glands or stomata, and in these is always double--one being on
each side of the limb--it is highly probable that the cutaneous gland is
in all cases composed of two cells of peculiar form, the line of union
being the longitudinal axis of the disk or pore.

"This areola, or nucleus of the cell as perhaps it might be termed,
is not confined to the epidermis, being also found, not only in the
pubescence of the surface, particularly when jointed, as in cypripedium,
but in many cases in the parenchyma or internal cells of the tissue,
especially when these are free from the deposition of granular matter.

"In the compressed cells of the epidermis the nucleus is in a
corresponding degree flattened; but in the internal tissue it is often
nearly spherical, more or less firmly adhering to one of the walls,
and projecting into the cavity of the cell. In this state it may not
unfrequently be found in the substance of the column and in that of the
perianthium.

"The nucleus is manifest also in the tissue of the stigma, where in
accordance with the compression of the utriculi, it has an intermediate
form, being neither so much flattened as in the epidermis nor so convex
as it is in the internal tissue of the column.

"I may here remark that I am acquainted with one case of apparent
exception to the nucleus being solitary in each utriculus or
cell--namely, in Bletia Tankervilliae. In the utriculi of the stigma of
this plant, I have generally, though not always, found a second areola
apparently on the surface, and composed of much larger granules than the
ordinary nucleus, which is formed of very minute granular matter, and
seems to be deep seated.

"Mr. Bauer has represented the tissue of the stigma, in the species of
Bletia, both before and, as he believes, after impregnation; and in the
latter state the utriculi are marked with from one to three areolae of
similar appearance.

"The nucleus may even be supposed to exist in the pollen of this family.
In the early stages of its formation, at least a minute areola is of
ten visible in the simple grain, and in each of the constituent parts
of cells of the compound grain. But these areolae may perhaps rather be
considered as merely the points of production of the tubes.

"This nucleus of the cell is not confined to orchideae, but is equally
manifest in many other monocotyledonous families; and I have even
found it, hitherto however in very few cases, in the epidermis of
dicotyledonous plants; though in this primary division it may perhaps
be said to exist in the early stages of development of the pollen. Among
monocotyledons, the orders in which it is most remarkable are Liliaceae,
Hemerocallideae, Asphodeleae, Irideae, and Commelineae.

"In some plants belonging to this last-mentioned family, especially
in Tradascantia virginica, and several nearly related species, it is
uncommonly distinct, not in the epidermis and in the jointed hairs of
the filaments, but in the tissue of the stigma, in the cells of the
ovulum even before impregnation, and in all the stages of formation
of the grains of pollen, the evolution of which is so remarkable in
tradascantia.

"The few indications of the presence of this nucleus, or areola, that I
have hitherto met with in the publications of botanists are chiefly in
some figures of epidermis, in the recent works of Meyen and Purkinje,
and in one case, in M. Adolphe Broigniart's memoir on the structure of
leaves. But so little importance seems to be attached to it that the
appearance is not always referred to in the explanations of the figures
in which it is represented. Mr. Bauer, however, who has also figured
it in the utriculi of the stigma of Bletia Tankervilliae has more
particularly noticed it, and seems to consider it as only visible after
impregnation."(2)


SCHLEIDEN AND SCHWANN AND THE CELL THEORY

That this newly recognized structure must be important in the economy of
the cell was recognized by Brown himself, and by the celebrated German
Meyen, who dealt with it in his work on vegetable physiology, published
not long afterwards; but it remained for another German, the professor
of botany in the University of Jena, Dr. M. J. Schleiden, to bring the
nucleus to popular attention, and to assert its all-importance in the
economy of the cell.

Schleiden freely acknowledged his indebtedness to Brown for first
knowledge of the nucleus, but he soon carried his studies of that
structure far beyond those of its discoverer. He came to believe that
the nucleus is really the most important portion of the cell, in that
it is the original structure from which the remainder of the cell is
developed. Hence he named it the cytoblast. He outlined his views in
an epochal paper published in Muller's Archives in 1838, under title of
"Beitrage zur Phytogenesis." This paper is in itself of value, yet the
most important outgrowth of Schleiden's observations of the nucleus did
not spring from his own labors, but from those of a friend to whom he
mentioned his discoveries the year previous to their publication.
This friend was Dr. Theodor Schwann, professor of physiology in the
University of Louvain.

At the moment when these observations were communicated to him Schwann
was puzzling over certain details of animal histology which he could
not clearly explain. His great teacher, Johannes Muller, had called
attention to the strange resemblance to vegetable cells shown by certain
cells of the chorda dorsalis (the embryonic cord from which the spinal
column is developed), and Schwann himself had discovered a corresponding
similarity in the branchial cartilage of a tadpole. Then, too, the
researches of Friedrich Henle had shown that the particles that make up
the epidermis of animals are very cell-like in appearance. Indeed, the
cell-like character of certain animal tissues had come to be matter of
common note among students of minute anatomy. Schwann felt that this
similarity could not be mere coincidence, but he had gained no clew to
further insight until Schleiden called his attention to the nucleus.
Then at once he reasoned that if there really is the correspondence
between vegetable and animal tissues that he suspected, and if the
nucleus is so important in the vegetable cell as Schleiden believed,
the nucleus should also be found in the ultimate particles of animal
tissues.

Schwann's researches soon showed the entire correctness of this
assumption. A closer study of animal tissues under the microscope
showed, particularly in the case of embryonic tissues, that "opaque
spots" such as Schleiden described are really to be found there
in abundance--forming, indeed, a most characteristic phase of the
structure. The location of these nuclei at comparatively regular
intervals suggested that they are found in definite compartments of the
tissue, as Schleiden had shown to be the case with vegetables; indeed,
the walls that separated such cell-like compartments one from another
were in some cases visible. Particularly was this found to be the case
with embryonic tissues, and the study of these soon convinced Schwann
that his original surmise had been correct, and that all animal tissues
are in their incipiency composed of particles not unlike the ultimate
particles of vegetables in short, of what the botanists termed cells.
Adopting this name, Schwann propounded what soon became famous as his
cell theory, under title of Mikroskopische Untersuchungen uber die
Ubereinstimmung in der Structur und dent Wachsthum der Thiere und
Pflanzen. So expeditious had been his work that this book was published
early in 1839, only a few months after the appearance of Schleiden's
paper.

As the title suggests, the main idea that actuated Schwann was to unify
vegetable and animal tissues. Accepting cell-structure as the basis of
all vegetable tissues, he sought to show that the same is true of animal
tissues, all the seeming diversities of fibre being but the alteration
and development of what were originally simple cells. And by cell
Schwann meant, as did Schleiden also, what the word ordinarily
implies--a cavity walled in on all sides. He conceived that the ultimate
constituents of all tissues were really such minute cavities, the most
important part of which was the cell wall, with its associated nucleus.
He knew, indeed, that the cell might be filled with fluid contents, but
he regarded these as relatively subordinate in importance to the wall
itself. This, however, did not apply to the nucleus, which was supposed
to lie against the cell wall and in the beginning to generate it.
Subsequently the wall might grow so rapidly as to dissociate itself
from its contents, thus becoming a hollow bubble or true cell; but the
nucleus, as long as it lasted, was supposed to continue in contact
with the cell wall. Schleiden had even supposed the nucleus to be a
constituent part of the wall, sometimes lying enclosed between two
layers of its substance, and Schwann quoted this view with seeming
approval. Schwann believed, however, that in the mature cell the nucleus
ceased to be functional and disappeared.

The main thesis as to the similarity of development of vegetable and
animal tissues and the cellular nature of the ultimate constitution
of both was supported by a mass of carefully gathered evidence which a
multitude of microscopists at once confirmed, so Schwann's work became
a classic almost from the moment of its publication. Of course various
other workers at once disputed Schwann's claim to priority of discovery,
in particular the English microscopist Valentin, who asserted, not
without some show of justice, that he was working closely along the same
lines. Put so, for that matter, were numerous others, as Henle, Turpin,
Du-mortier, Purkinje, and Muller, all of whom Schwann himself had
quoted. Moreover, there were various physiologists who earlier than
any of these had foreshadowed the cell theory--notably Kaspar Friedrich
Wolff, towards the close of the previous century, and Treviranus about
1807, But, as we have seen in so many other departments of science, it
is one thing to foreshadow a discovery, it is quite another to give
it full expression and make it germinal of other discoveries. And when
Schwann put forward the explicit claim that "there is one universal
principle of development for the elementary parts, of organisms, however
different, and this principle is the formation of cells," he enunciated
a doctrine which was for all practical purposes absolutely new and
opened up a novel field for the microscopist to enter. A most important
era in physiology dates from the publication of his book in 1839.


THE CELL THEORY ELABORATED

That Schwann should have gone to embryonic tissues for the establishment
of his ideas was no doubt due very largely to the influence of the great
Russian Karl Ernst von Baer, who about ten years earlier had published
the first part of his celebrated work on embryology, and whose ideas
were rapidly gaining ground, thanks largely to the advocacy of a few
men, notably Johannes Muller, in Germany, and William B. Carpenter, in
England, and to the fact that the improved microscope had made minute
anatomy popular. Schwann's researches made it plain that the best
field for the study of the animal cell is here, and a host of explorers
entered the field. The result of their observations was, in the main,
to confirm the claims of Schwann as to the universal prevalence of the
cell. The long-current idea that animal tissues grow only as a sort
of deposit from the blood-vessels was now discarded, and the fact of
so-called plantlike growth of animal cells, for which Schwann contended,
was universally accepted. Yet the full measure of the affinity between
the two classes of cells was not for some time generally apprehended.

Indeed, since the substance that composes the cell walls of plants is
manifestly very different from the limiting membrane of the animal cell,
it was natural, so long as the wall was considered the most essential
part of the structure, that the divergence between the two classes
of cells should seem very pronounced. And for a time this was the
conception of the matter that was uniformly accepted. But as time
went on many observers had their attention called to the peculiar
characteristics of the contents of the cell, and were led to ask
themselves whether these might not be more important than had been
supposed. In particular, Dr. Hugo von Mohl, professor of botany in the
University of Tubingen, in the course of his exhaustive studies of
the vegetable cell, was impressed with the peculiar and characteristic
appearance of the cell contents. He observed universally within the cell
"an opaque, viscid fluid, having granules intermingled in it," which
made up the main substance of the cell, and which particularly impressed
him because under certain conditions it could be seen to be actively in
motion, its parts separated into filamentous streams.

Von Mohl called attention to the fact that this motion of the cell
contents had been observed as long ago as 1774 by Bonaventura Corti,
and rediscovered in 1807 by Treviranus, and that these observers had
described the phenomenon under the "most unsuitable name of 'rotation
of the cell sap.'" Von Mohl recognized that the streaming substance was
something quite different from sap. He asserted that the nucleus of the
cell lies within this substance and not attached to the cell wall as
Schleiden had contended. He saw, too, that the chlorophyl granules,
and all other of the cell contents, are incorporated with the "opaque,
viscid fluid," and in 1846 he had become so impressed with the
importance of this universal cell substance that he gave it the name
of protoplasm. Yet in so doing he had no intention of subordinating the
cell wall. The fact that Payen, in 1844, had demonstrated that the
cell walls of all vegetables, high or low, are composed largely of one
substance, cellulose, tended to strengthen the position of the cell wall
as the really essential structure, of which the protoplasmic contents
were only subsidiary products.

Meantime, however, the students of animal histology were more and more
impressed with the seeming preponderance of cell contents over cell
walls in the tissues they studied. They, too, found the cell to be
filled with a viscid, slimy fluid capable of motion. To this Dujardin
gave the name of sarcode. Presently it came to be known, through the
labors of Kolliker, Nageli, Bischoff, and various others, that there are
numerous lower forms of animal life which seem to be composed of this
sarcode, without any cell wall whatever. The same thing seemed to be
true of certain cells of higher organisms, as the blood corpuscles.
Particularly in the case of cells that change their shape markedly,
moving about in consequence of the streaming of their sarcode, did it
seem certain that no cell wall is present, or that, if present, its role
must be insignificant.

And so histologists came to question whether, after all, the cell
contents rather than the enclosing wall must not be the really essential
structure, and the weight of increasing observations finally left no
escape from the conclusion that such is really the case. But attention
being thus focalized on the cell contents, it was at once apparent
that there is a far closer similarity between the ultimate particles of
vegetables and those of animals than had been supposed. Cellulose and
animal membrane being now regarded as more by-products, the way was
clear for the recognition of the fact that vegetable protoplasm and
animal sarcode are marvellously similar in appearance and general
properties. The closer the observation the more striking seemed this
similarity; and finally, about 1860, it was demonstrated by Heinrich de
Bary and by Max Schultze that the two are to all intents and purposes
identical. Even earlier Remak had reached a similar conclusion, and
applied Von Mohl's word protoplasm to animal cell contents, and now this
application soon became universal. Thenceforth this protoplasm was
to assume the utmost importance in the physiological world, being
recognized as the universal "physical basis of life," vegetable and
animal alike. This amounted to the logica

Showing first 200,000 characters. Full text: gutenberg.org/ebooks/1708