Physiology and Hygiene for Secondary Schools
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Title: Physiology and Hygiene for Secondary Schools
Author: Francis M. Walters
Release date: November 15, 2005 [eBook #18779]
Most recently updated: June 26, 2020
Language: English
Other information and formats: www.gutenberg.org/ebooks/18779
*** START OF THE PROJECT GUTENBERG EBOOK PHYSIOLOGY AND HYGIENE FOR SECONDARY SCHOOLS ***
Physiology and Hygiene for Secondary Schools
by Francis M. Walters, A.M.
Edition 1, (November 15, 2005)
D.C. Heath and Co. - Publishers
Original copyright 1909
"It is quite possible to give instruction in this subject in such
a manner as not only to confer knowledge which is useful in
itself, but to serve the purpose of a training in accurate
observation, and in the methods of reasoning of physical
science."--_Huxley._
PREFACE
The aim in the preparation of this treatise on the human body has been,
first, to set forth in a _teachable_ manner the actual science of
physiology; and second, to present the facts of hygiene largely as
_applied physiology_. The view is held that "right living" consists in the
harmonious adjustment of one's habits to the nature and plan of the body,
and that the best preparation for such living is a correct understanding
of the physical self. It is further held that the emphasizing of
physiology augments in no small degree the educative value of the subject,
greater opportunity being thus afforded for exercise of the reasoning
powers and for drill in the _modus operandi_ of natural forces. In the
study of physiology the facts of anatomy have a place, but in an
elementary course these should be restricted to such as are necessary for
revealing the general structure of the body.
Although no effort has been spared to bring this work within the
comprehension of the pupil, its success in the classroom will depend
largely upon the method of handling the subject by the teacher. It is
recommended, therefore, that the _relations_ which the different organs
and processes sustain to each other, and to the body as a whole, be given
special prominence. The pupil should be impressed with the essential unity
of the body and should see in the diversity of its activities the serving
of a common purpose. In creating such an impression the introductory
paragraphs at the beginning of many of the chapters and the summaries
throughout the book, as well as the general arrangement of the
subject-matter, will be found helpful.
Since the custom largely prevails of teaching physiology in advance of the
sciences upon which it rests--biology, physics, and chemistry--care should
be exercised to develop correct ideas of the principles and processes
derived from these sciences. Too much latitude has been taken in the past
in the use of comparisons and illustrations drawn from "everyday life." To
teach that the body is a "house," "machine," or "city"; that the nerves
carry "messages"; that the purpose of oxygen is to "burn up waste"; that
breathing is to "purify the blood," etc., may give the pupil phrases which
he can readily repeat, but teaching of this kind does not give him correct
ideas of his body.
The method of teaching, however, that uses the pupil's experience as a
basis upon which to build has a value not to be overlooked. The fact that
such expressions as those quoted above are so easily remembered proves the
value of connecting new knowledge with the pupil's experience. But _the
inadequacy of this experience must be recognized_ and taken into account.
The concepts of the average pupil are entirely too indefinite and limited
to supply the necessary _foundation for a science_ such as physiology.
Herein lies the great value of experiments and observations. They
supplement the pupil's experience, and increase both the number and
definiteness of his concepts. No degree of success can be attained if this
phase of the study is omitted.
The best results in physiology teaching are of course attained where
laboratory work is carried on by the pupils, but where this cannot be
arranged, class experiments and observations must suffice. The Practical
Work described at the close of most of the chapters is mainly for class
purposes. While these serve a necessary part in the development of the
subject, it is not essential that all of the experiments and observations
be made, the intention being to provide for some choice on the part of the
teacher. A note-book should be kept by the pupil.
To adapt the book to as wide a range of usefulness as possible, more
subject-matter is introduced than is usually included in an elementary
course. Such portions, however, as are unessential to a proper
understanding of the body by the pupil are set in small type, to be used
at the discretion of the teacher.
The use of books of reference is earnestly recommended. For this purpose
the usual high school texts may be employed to good advantage. A few more
advanced works should, however, be frequently consulted. For this purpose
Martin's _Human Body_ (Advanced Course), Rettger's _Advanced Lessons in
Physiology_, Thornton's _Human Physiology_, Huxley's _Lessons in
Elementary Physiology_, Howell's _A Text-book of Physiology_, Hough and
Sedgwick's _Hygiene and Sanitation_, and Pyle's _Personal Hygiene_ will be
found serviceable.
In the preparation of this work valuable assistance has been rendered by
Dr. C.N. McAllister, Department of Psychology, and by Professor B.M.
Stigall, Department of Biology, along the lines of their respective
specialties, and in a more general way by President W.J. Hawkins and
others of the Warrensburg, Missouri, State Normal School. Expert advice
from Professor S.D. Magers, Instructor in Physiology and Bacteriology,
State Normal School, Ypsilanti, Michigan, has been especially helpful, and
many practical suggestions from the high school teachers of physiology of
Kansas City, Missouri, Professor C.H. Nowlin, Central High School, Dr.
John W. Scott, Westport High School, and Professor A.E. Shirling, Manual
Training High School, all of whom read both manuscript and proofs, have
been incorporated. Considerable material for the Practical Work, including
the respiration experiment (page 101) and the reaction time experiment
(page 323), were contributed by Dr. Scott. Professor Nowlin's suggestions
on subject-matter and methods of presentation deserve special mention. To
these and many others the author makes grateful acknowledgment.
F.M.W.
MISSOURI STATE NORMAL SCHOOL,
SECOND DISTRICT, May 1, 1909.
CONTENTS
Preface
Contents
PART I: THE VITAL PROCESSES
CHAPTER I - INTRODUCTION
CHAPTER II - GENERAL VIEW OF THE BODY
CHAPTER III - THE BODY ORGANIZATION
CHAPTER IV - THE BLOOD
CHAPTER V - THE CIRCULATION
CHAPTER VI - THE LYMPH AND ITS MOVEMENT THROUGH THE BODY
CHAPTER VII - RESPIRATION
CHAPTER VIII - PASSAGE OF OXYGEN THROUGH THE BODY
CHAPTER IX - FOODS AND THE THEORY OF DIGESTION
CHAPTER X - ORGANS AND PROCESSES OF DIGESTION
CHAPTER XI - ABSORPTION, STORAGE, AND ASSIMILATION
CHAPTER XII - ENERGY SUPPLY OF THE BODY
CHAPTER XIII - GLANDS AND THE WORK OF EXCRETION
PART II: MOTION, COORDINATION, AND SENSATION
CHAPTER XIV - THE SKELETON
CHAPTER XV - THE MUSCULAR SYSTEM
CHAPTER XVI - THE SKIN
CHAPTER XVII - STRUCTURE OF THE NERVOUS SYSTEM
CHAPTER XVIII - PHYSIOLOGY OF THE NERVOUS SYSTEM
CHAPTER XIX - HYGIENE OF THE NERVOUS SYSTEM
CHAPTER XX - PRODUCTION OF SENSATIONS
CHAPTER XXI - THE LARYNX AND THE EAR
CHAPTER XXII - THE EYE
CHAPTER XXIII - THE GENERAL PROBLEM OF KEEPING WELL
APPENDIX
INDEX
PHYSIOLOGY AND HYGIENE
PART I: THE VITAL PROCESSES
CHAPTER I - INTRODUCTION
To derive strength equal to the daily task; to experience the advantages
of health and avoid the pain, inconvenience, and danger of disease; to
live out contentedly and usefully the natural span of life: these are
problems that concern all people. They are, however, but different phases
of one great problem--the problem of properly managing or caring for the
body. To supply knowledge necessary to the solution of this problem is the
chief reason why the body is studied in our public schools.
*Divisions of the Subject.*--The body is studied from three standpoints:
structure, use of parts, and care or management. This causes the main
subject to be considered under three heads, known as anatomy, physiology,
and hygiene.
_Anatomy_ treats of the construction of the body--the parts which compose
it, what they are like, and where located. Its main divisions are known as
gross anatomy and histology. _Gross anatomy_ treats of the larger
structures of the body, while _histology_ treats of the minute structures
of which these are composed--parts too small to be seen with the naked eye
and which have to be studied with the aid of the microscope.
_Physiology_ treats of the function, or use, of the different parts of the
body--the work which the parts do and how they do it--and of their relations
to one another and to the body as a whole.
_Hygiene_ treats of the proper care or management of the body. In a
somewhat narrower sense it treats of the "laws of health." Hygiene is said
to be _personal_, when applied by the individual to his own body;
_domestic_, when applied to a small group of people, as the family; and
public, or _general_, when applied to the community as a whole or to the
race.
*The General Aim of Hygiene.*--There are many so-called laws of health, and
for these laws it is essential in the management of the body to find a
common basis. This basic law, suggested by the nature of the body and
conditions that affect its well-being, may be termed the _Law of Harmony:
The mode of living must harmonize with the plan of the body_. To live
properly one must supply the conditions which his body, on account of its
nature and plan, requires. On the other hand, he must avoid those things
and conditions which are injurious, _i.e._, out of harmony with the body
plan. To secure these results, it is necessary to determine what is and
what is not in harmony with the plan of the body, and to find the means of
applying this knowledge to the everyday problems of living. Such is the
general aim of hygiene. Stated in other words: Hygiene has for its general
aim the bringing about of an essential harmony between the body and the
things and conditions that affect it.(1)
*Relation of Anatomy and Physiology to the Study of Hygiene.*--If the chief
object in studying the body is that of learning how to manage or care for
it, and hygiene supplies this information, why must we also study anatomy
and physiology? The answer to this question has already been in part
suggested. In order to determine what things and conditions are in harmony
with the plan of the body, we must know what that plan is. This knowledge
is obtained through a study of anatomy and physiology. The knowledge
gained through these subjects also renders the study of hygiene more
interesting and valuable. One is enabled to see _why_ and _how_ obedience
to hygienic laws benefits, and disobedience to them injures, the body.
This causes the teachings of hygiene to be taken more seriously and
renders them more practical. In short, anatomy and physiology supply a
necessary basis for the study of hygiene.
*Advantages of Properly Managing the Body.*--One result following the
mismanagement of the body is loss of health. But attending the loss of
health are other results which are equally serious and far-reaching.
Without good health, people fail to accomplish their aims and ambitions in
life; they miss the joy of living; they lose their ability to work and
become burdens on their friends or society. The proper management of the
body means health, and it also means the capacity for work and for
enjoyment. Not only should one seek to preserve his health from day to
day, but he should so manage his body as to use his powers to the best
advantage and prolong as far as possible the period during which he may be
a capable and useful citizen.
CHAPTER II - GENERAL VIEW OF THE BODY
*External Divisions.*--Examined from the outside, the body presents certain
parts, or divisions, familiar to all. The main, or central, portion is
known as the _trunk_, and to this are attached the _head_, the _upper
extremities_, and the _lower extremities_. These in turn present smaller
divisions which are also familiar. The upper part of the trunk is known as
the _thorax_, or chest, and the lower part as the _abdomen_. The portions
of the trunk to which the arms are attached are the _shoulders_, and those
to which the legs are joined are the _hips_, while the central rear
portion between the neck and the hips is the _back_. The fingers, the
hand, the wrist, the forearm, the elbow, and the upper arm are the main
divisions of each of the upper extremities. The toes, the foot, the ankle,
the lower leg, the knee, and the thigh are the chief divisions of each of
the lower extremities. The head, which is joined to the trunk by the neck,
has such interesting parts as the eyes, the ears, the nose, the jaws, the
cheeks, and the mouth. The entire body is inclosed in a double covering,
called the _skin_, which protects it in various ways.
*The Tissues.*--After examining the external features of the body, we
naturally inquire about its internal structures. These are not so easily
investigated, and much which is of interest to advanced students must be
omitted from an elementary course. We may, however, as a first step in
this study, determine what kinds of materials enter into the construction
of the body. For this purpose the body of some small animal should be
dissected and studied. (See observation at close of chapter.) The
different materials found by such a dissection correspond closely to the
substances, called _tissues_, which make up the human body. The main
tissues of the body, as ordinarily named, are the _muscular_ tissue, the
_osseous_ tissue, the _connective_ tissue, the _nervous_ tissue, the
_adipose_ tissue, the _cartilaginous_ tissue, and the _epithelial_ and
_glandular_ tissue. Most of these present different varieties, making all
together some fifteen different kinds of tissues that enter into the
construction of the body.(2)
*General Purposes of the Tissues.*--The tissues, first of all, _form the
body_. As a house is constructed of wood, stone, plaster, iron, and other
building materials, so is the body made up of its various tissues. For
this reason the tissues have been called the _building materials_ of the
body.
In addition to forming the body, the tissues supply the means through
which its work is carried on. They are thus the _working materials_ of the
body. In serving this purpose the tissues play an active role. All of them
must perform the activities of growth and repair, and certain ones (the
so-called active tissues) must do work which benefits the body as a whole.
*Purposes of the Different Tissues.*--In the construction of the body and
also in the work which it carries on, the different tissues are made to
serve different purposes. The osseous tissue is the chief substance in the
bony framework, or skeleton, while the muscular tissue produces the
different movements of the body. The connective tissue, which is
everywhere abundant, serves the general purpose of connecting the
different parts together. Cartilaginous tissue forms smooth coverings over
the ends of the bones and, in addition to this, supplies the necessary
stiffness in organs like the larynx and the ear. The nervous tissue
controls the body and brings it into proper relations with its
surroundings, while the epithelial tissue (found upon the body surfaces
and in the glands) supplies it with protective coverings and secretes
liquids. The adipose tissue (fat) prevents the too rapid escape of heat
from the body, supplies it with nourishment in time of need, and forms
soft pads for delicate organs like the eyeball.
*Properties of the Tissues.*--If we inquire how the tissues are able to
serve such widely different purposes, we find this answer. The tissues
differ from one another both in composition and in structure and, on this
account, differ in their properties.(3) Their different properties enable
them to serve different purposes in the body. Somewhat as glass is adapted
by its transparency, hardness, and toughness to the use made of it in
windows, the special properties of the tissues adapt them to the kinds of
service which they perform. Properties that adapt tissues to their work in
the body are called _essential_ properties. The most important of these
essential properties are as follows:
1. Of osseous tissue, hardness, stiffness, and toughness. 2. Of muscular
tissue, contractility and irritability. 3. Of nervous tissue, irritability
and conductivity. 4. Of cartilaginous tissue, stiffness and elasticity. 5.
Of connective tissue, toughness and pliability. 6. Of epithelial tissue,
ability to resist the action of external forces and power to secrete.
[Fig. 1]
Fig. 1--Hand and forearm, showing the grouping of muscular and connective
tissues in the organ for grasping.
*Tissue Groups.*--In the construction of the body the tissues are grouped
together to form its various divisions or parts. A group of tissues which
serves some special purpose is known as an _organ_. The hand, for example,
is an organ for grasping (Fig. 1). While the different organs of the body
do not always contain the same tissues, and never contain them in the same
proportions, they do contain such tissues as their work requires and these
have a special arrangement--one adapted to the work which the organs
perform.
In addition to forming the organs, the tissues are also grouped in such a
manner as to provide supports for organs and to form cavities in which
organs are placed. The various cavities of the body are of particular
interest and importance. The three largest ones are the _cranial_ cavity,
containing the brain; the _thoracic_ cavity, containing the heart and the
lungs; and the _abdominal_ cavity, containing the stomach, the liver, the
intestines, and other important organs (Fig. 2). Smaller cavities serving
different purposes are also found.
[Fig. 2]
Fig. 2--Diagram of a lengthwise section of the body to show its large
cavities and the organs which they contain.
*Organs and Systems.*--The work of the body is carried on by its various
organs. Many, in fact the majority, of these organs serve more than one
purpose. The tongue is used in talking, in masticating the food, and in
swallowing. The nose serves at least three distinct purposes. The mouth,
the arms, the hands, the feet, the legs, the liver, the lungs, and the
stomach are also organs that serve more than one purpose. This introduces
the principle of economy into the construction of the body and diminishes
the number of organs that would otherwise be required.
The various organs also _combine_ with one another in carrying on the work
of the body. An illustration of this is seen in the digestion of the
food--a process which requires the combined action of the mouth, stomach,
liver, intestines, and other organs. A number of organs working together
for the same purpose form a _system_. The chief systems of the body are
the digestive system, the circulatory system, the respiratory system, the
muscular system, and the nervous system.
*The Organ and its Work.*--A most interesting question relating to the work
of the organ is this: Does the organ work for its own benefit or for the
benefit of the body as a whole? Does the hand, for example, grasp for
itself or in order that the entire body may come into possession? Only
slight study is sufficient to reveal the fact that each organ performs a
work which benefits the body as a whole. In other words, just as the organ
itself is a part of the body, the work which it does is a part of the
necessary work which the body has to do.
But in working for the general good, or for the body as a whole, each
organ becomes a sharer in the benefits of the work done by every other
organ. While the hand receives only a little of the nourishment contained
in the food which it places in the mouth or of the heat from, fuel which
it places on the fire, it is aided and supported by the work of all the
other organs of the body--eyes, feet, brain, heart, etc. The hand does not
and cannot work independently of the other organs. It is one of the
partners in a very close combination where, by doing a particular work,
it, shares in the profits of all. What is true of the hand is true of
every other organ of the body.
*An Organization.*--The relations which the different organs sustain to
each other and to the body as a whole suggest the possibility of
classifying the body as an organization. This term is broadly applied to a
variety of combinations. An organization is properly defined as _any group
of individuals which, in working together for a common purpose, practices
the division of labor_. This definition will be better understood by
considering a few familiar examples.
A baseball team is an organization. The team is made up of individual
players. These work together for the common purpose of winning games. They
practice the division of labor in that the different players do different
things--one catching, another pitching, and so on. A manufacturing
establishment which employs several workmen may also be an organization.
The article manufactured provides the common purpose toward which all
strive; and, in the assignment of different kinds of work to the
individual workmen, the principle of division of labor is carried out. For
the same reason a school, a railway system, an army, and a political party
are organizations.
An organization of a lower order of individuals than these human
organizations is to be found in a hive of bees. This is made up of the
individual bees, and these, in carrying on the general work of the hive,
are known to practice the division of labor.
*Is the Body an Organization*?--If the body is an organization, it must
fulfill the conditions of the definition. It must be made up of separate
or individual parts. These must work together for the same general
purpose, and, in the accomplishment of this purpose, must practice the
division of labor. That the body practices the division of labor is seen
in the related work of the different organs. That it is made up of minute,
but individual, parts will be shown in the chapter following. That it
carries on a _general work_ which is accomplished through the combined
action of its individual parts is revealed through an extended study of
its various activities. _The body is an organization._ Moreover, it is one
of the most complex and, at the same time, most perfect of the
organizations of which we have knowledge.
*Summary.*--Viewed from the outside, the body is seen to be made up of
divisions which are more or less familiar. Viewed internally, it is found
to consist of different kinds of materials, called tissues. The tissues
are adapted, by their properties, to different purposes both in the
construction of the body and in carrying on its work. The working parts of
the body are called organs and these in their work combine to form
systems. The entire body, on account of the method of its construction and
the character of its work, may be classed as an organization.
*Exercises.*--1. Name and locate the chief external divisions of the body.
2. What tissues may be found by dissecting the leg of a chicken?
3. Name the most important properties and the most important uses of
muscular tissue, osseous tissue, and connective tissue.
4. Define an organ. Define a system. Name examples of each.
5. Name the chief cavities of the body and the organs which they contain.
6. What tissues are present in the hand? How does each of these aid in the
work of the hand?
7. Define an organization. Show that a railway system, an army, and a
school are organizations.
8. What is meant by the phrase "division of labor"? In what manner is the
division of labor practiced in a shoe or watch factory? What are the
advantages?
9. What are the proofs that the body is an organization?
PRACTICAL WORK
*Observation on the Tissues.*--Examine with care the structures in the
entire leg of a chicken, squirrel, rabbit, or other small animal used for
food. Observe, first of all, the external covering, consisting of cuticle
and hair, claws, scales, or feathers, according to the specimen. These are
similar in structure, and they form the epidermis, which is one kind of
_epithelial_ tissue. With a sharp knife lay open the skin and observe that
it is attached to the parts underneath by thin, but tough, threads and
sheaths. These represent a variety of _connective_ tissue. The reddish
material which forms the greater portion of the specimen is a variety of
_muscular_ tissue, and its divisions are called muscles. With a blunt
instrument, separate the muscles, by tearing apart the connective tissue
binding them together, and find the glistening white strips of connective
tissue (tendons) which attach them to the bones. Find near the central
part of the leg a soft, white cord (a nerve) which represents one variety
of _nervous_ tissue. The bones, which may now be examined, form the
_osseous_ tissue. At the ends of the bones will be found a layer of
smooth, white material which represents one kind of _cartilaginous_
tissue. The _adipose_, or fatty, tissue, which is found under the skin and
between the other tissues, is easily recognized.
*Relation of the Tissues to the Organs.*--Observe in the specimen just
studied the relation of the different tissues to the organ as a whole
(regarding the leg as an organ), _i.e._, show how each of the tissues aids
in the work which the organ accomplishes. Show in particular how the
muscles supply the foot with motion, by tracing out the tendons that
connect them with the toes. Pull on the different tendons, noting the
effect upon the different parts of the foot.
CHAPTER III - THE BODY ORGANIZATION
What is the nature of the body organization? What are the individual
parts, or units, that make it up? What general work do these carry on and
upon what basis do they practice the division of labor? The answers to
these questions will suggest the main problems in the study of the body.
[Fig. 3]
Fig. 3--Diagram showing the relation of the cells and the intercellular
material. _C._ Cells. _I._ Intercellular material.
*Complex Nature of the Tissues.*--To the unaided eye the tissues have the
appearance of simple structures. The microscope, however, shows just the
reverse to be true. When any one of the tissues is suitably prepared and
carefully examined with this instrument, at least two classes of materials
can be made out. One of these consists of minute particles, called
_cells_; the other is a substance lying between the cells, known as the
_intercellular material_ (Fig. 3). The cells and the intercellular
material, though varying in their relative proportions, are present in all
the tissues.
*The Body a Cell Group.*--The biologist has found that the bodies of all
living things, plants as well as animals, consist either of single cells
or of groups of cells. The single cells live independently of one another,
but the cells that form groups are attached to, and are more or less
dependent upon, one another. In the first condition are found the very
lowest forms of life. In the second, life reaches its greatest
development. The body of man, which represents the highest type of life,
is recognized as a group of cells. In this group each cell is usually
separate and distinct from the others, but is attached to them, and is
held in place by the intercellular material.
*Protoplasm, the Cell Substance.*--The cell is properly regarded as an
_organized_ bit of a peculiar material, called _protoplasm_. This is a
semi-liquid and somewhat granular substance which resembles in appearance
the white of a raw egg. Its true nature and composition are unknown,
because any attempt to analyze it kills it, and dead protoplasm is
essentially different from living protoplasm. It is known, however, to be
a highly complex substance and to undergo chemical change readily. It
appears to be the only kind of matter with which life is ever associated,
and for this reason protoplasm is called the _physical basis of life_. Its
organization into separate bits, or cells, is necessary to the life
activities that take place within it.
*Structure of the Cell.*--Though all portions of the cell are formed from
the protoplasm, this essential substance differs both in structure and in
function at different places in the cell. For this reason the cell is
looked upon as a complex body having several distinct parts. At or near
the center is a clear, rounded body, called the _nucleus_. This plays some
part in the nourishment of the cell and also in the formation of new
cells. If it be absent, as is sometimes the case, the cell is short-lived
and unable to reproduce itself. The variety of protoplasm contained in the
nucleus is called the _nucleoplasm_.
[Fig. 4]
Fig. 4--Diagram of a typical cell (after Wilson). 1. Main body. 2. Nucleus.
3. Attraction sphere. 4. Food particles and waste. 5. Cell-wall. 6. Masses
of active material found in certain cells, called plastids.
Surrounding the nucleus is the _main body_ of the cell, sometimes referred
to as the "protoplasm." Since the protoplasm forms all parts of the cell,
this substance is more properly called the _cytoplasm_, or cell plasm.
Surrounding and inclosing the cytoplasm, in many cells, is a thin outer
layer, or membrane, which affords more or less protection to the contents
of the cell. This is usually referred to as the _cell-wall_. A fourth part
of the cell is also described, being called the _attraction sphere_. This
is a small body lying near the nucleus and cooeperating with that body in
the formation of new cells. Food particles, wastes, and other substances
may also be present in the cytoplasm. The parts of a typical cell are
shown in Fig. 4.
*Importance of the Cells.*--The cells must be regarded as the living,
working parts of the body. They are the active agents in all of the
tissues, enabling them to serve their various purposes. Working through
the tissues, they build up the body and carry on its different activities.
They are recognized on this account as _the units of structure and of
function_, and are the "individuals" in the body organization. Among the
most important and interesting of the activities of the cells are those by
which they build up the body, or cause it to grow.
*How the Cells enable the Body to Grow.*--Every cell is able to take new
material into itself and to add this to the protoplasm. This tends to
increase the amount of the protoplasm, thereby causing the cells to
increase in size. A general increase in the size of the cells has the
effect of increasing the size of the entire body, and this is one way by
which they cause it to grow. There is, however, a fixed limit, varying
with different cells, to the size which they attain, and this is quite
low. (The largest cells are scarcely visible to the naked eye.) Any marked
increase in the size of the body must, therefore, be brought about by
other means. Such a means is found in the formation of new cells, or _cell
reproduction_. The new cells are always formed _by_ and _from_ the old
cells, the essential process being known as _cell-division_.
[Fig. 5]
Fig. 5--Steps in cell-division (after Wilson). Note that the process begins
with the division of the attraction sphere, then involves the nucleus, and
finally separates the main body.
*Cell-Division.*--By dividing, a single cell will, on attaining its growth,
separate into two or more new cells. The process is quite complex and is
imperfectly understood. It is known, however, that the act of separation
is preceded by a series of changes in which the attraction sphere and the
nucleus actively participate, and that, as a result of these changes, the
contents of the old cell are rearranged to form the new cells. Some of the
different stages in the process, as they have been studied under the
microscope, are indicated in Fig. 5.
Gradually, through the formation of new cells and by the growth of these
cells after they have been formed, the body attains its full size. When
growth is complete, cell reproduction is supposed to cease except where
the tissues are injured, as in the breaking of a bone, or where cells,
like those at the surface of the skin, are subject to wear. Then new
material continues to be added to the protoplasm throughout life, but in
amount only sufficient to replace that lost from the protoplasm as waste.
[Fig. 6]
Fig. 6--A tumbler partly filled with marbles covered with water, suggesting
the relations of the cells to the lymph.
*Cell Surroundings.*--All cells are said to be _aquatic_. This means simply
that they require water for carrying on their various activities. The
cells, in order to live, must take in and give out materials, and water is
necessary to both processes. It is also an essential part of the
protoplasm. Deprived of water, cells become inactive and usually die.
Aquatic surroundings are provided for the cells of the body through a
liquid known as the _lymph_, which is distributed throughout the
intercellular material (Fig. 6). This consists of water containing oxygen
and food substances in solution. Besides supplying these to the cells, the
lymph also receives their wastes. Through the lymph the necessary
conditions for cell life are provided in the body.
*The General Work of Cells.*--In handling the materials derived from the
lymph, the cells carry on three well-defined processes, known as
absorption, assimilation, and excretion.
_Absorption_ is the process of taking water, food, and oxygen into the
cells.
_Assimilation_ is a complex process which results in the addition of the
absorbed materials to the protoplasm. Through assimilation the protoplasm
is built up or renewed.
_Excretion_ is the throwing off of such waste materials as have been
formed in the cells. These are passed into the lymph and thence to the
surface of the body.
Absorption, assimilation, excretion, and also reproduction are performed
by all classes of cells. They are, on this account, referred to as the
_general work of cells_.
*The Special Work of Cells.*--In addition to the general work which all
cells do in common, each class of cells in the body is able to do some
particular kind of work--a work which the others cannot do or which they
can do only to a limited extent. This is spoken of as the _special work of
cells_. Examples of the special work of cells are found in the production
of motion by muscle cells and in the secretion of liquids by gland cells.
It may be noted that while the general work of cells benefits them
individually, their special work benefits the body as a whole. Another
example of the special work of cells is found in the
[Fig. 7]
Fig. 7--Cartilage cells, surrounded by the intercellular material which
they have deposited.
*Production of the Intercellular Material.*--Though most of the cells of
the body deposit to a slight extent this material, the greater part of it
is produced by a single class of cells found in bone, cartilage, and
connective tissue. Cartilage, bone, and connective tissue differ greatly
from the other tissues in the amount of intercellular material which they
contain, the difference being due to these cells. In the connective tissue
they deposit the fibrous material so important in holding the different
parts of the body together. In the cartilage they produce the gristly
substance which forms by far its larger portion (Fig. 7). In the bones
they deposit a material similar to that in the cartilage, except that with
it is mixed a mineral substance which gives the bones their hardness and
stiffness.(4) The intercellular material, in addition to connecting the
cells, supplies to certain tissues important properties, such as the
elasticity of cartilage and the stiffness of the bones.
*Nature of the Body Organization.*--The division of labor carried on by the
different organs, as shown in the preceding chapter, is in reality carried
on by the cells that form the organs. To see that this is true we have
only to observe the relation of cells to tissues and of tissues to organs.
The cells form the tissues and the tissues form the organs. This
arrangement enables the special work of different kinds of cells to be
combined in the work of the organ as a whole. This is seen in the hand
which, in grasping, uses motion supplied by the muscle cells, a
controlling influence supplied by the nerve cells, a framework supplied by
the bone cells, and so on. The cells supply the basis for the body
organization and, properly speaking, the body is _an organization of
cells_(5) (Recall the definition of an organization, page 10.) In this
organization there are to be observed:
1. A definite arrangement of the cells to form the tissues. A tissue is a
group of like cells.
2. A definite arrangement of the tissues in the organ. Each organ contains
the tissues needed for its work.
3. In several instances there is a definite arrangement of organs to form
systems.
4. The body as a whole is made up of organs and systems, together with the
structures necessary for their support and protection.
There now remains a further question for consideration. What is the one
supreme end, or purpose, toward which all the activities of the body
organization are directed? This purpose will naturally have some relation
to the maintenance, or preservation, of the cell group which we call the
body.
*The Maintenance of Life.*--The preservation of any cell group in its
natural condition, whether it be plant or animal, is accomplished through
keeping it alive. If life ceases, the group quickly disintegrates and its
elements become scattered, a fact which is verified through everyday
observation. Though the nature of life is unknown, it may be looked upon
as the organizer and preserver of the protoplasm. But in preserving the
protoplasm it also preserves the entire cell group, or body. Life is thus
the most essential condition of the body. _With life all portions of the
body are concerned, and toward its maintenance all the activities of the
body organization are directed_.
*The Nutrient Fluid in its Relations to the Cells.*--The maintenance of
life within the cells requires, as we have seen, that they be supplied
with water, food, and oxygen, and that they be relieved of such wastes as
they form. This double purpose is accomplished through the agency of an
internal nutrient fluid, a portion of which has already been referred to
as the lymph. Not only does this fluid supply the means for keeping the
cells alive, but, through the cells, it is also the means of preserving
the life of the body as a whole.
The cells, however, rapidly exhaust the nutrient fluid. They take from it
food and oxygen and they put into it their wastes. To prevent its becoming
unfit for supplying their needs, food and oxygen must be continually added
to this fluid, and waste materials must be continually removed. This is
not an easy task. As a matter of fact, the preparation, distribution, and
purification of the nutrient fluid requires the direct or indirect aid of
practically all parts of the body. It supplies for this reason a broad
basis for the division of labor on the part of the cells.
*Relation of the Body to its Environment.*--While life is directly
dependent upon the internal nutrient fluid, it is indirectly dependent
upon the physical surroundings of the body. Herein lies the need of the
_external_ organs--the feet and legs for moving about, the hands for
handling things, the eyes for directing movements, etc. That the great
needs of the body are supplied from its surroundings are facts of common
experience. Food, shelter, air, clothing, water, and the means of
protection are external to the body and form a part of its environment. In
making the things about him contribute to his needs, man encounters a
problem which taxes all his powers. Only by toil and hardship, "by the
sweat of his brow," has he been able to wrest from his surroundings the
means of his sustenance.
*The Main Physiological Problems.*--The study of the body is thus seen to
resolve itself naturally into the consideration of two main problems:
1. _That of maintaining in the body a nutrient fluid for the cells._
2. _That of bringing the body into such relations with its surroundings as
will enable it to secure materials for the nutrient fluid and satisfy its
other needs._
The first problem is _internal_ and includes the so-called vital
processes, known as digestion, circulation, respiration, and excretion.
The second problem is _external_, as it were, and includes the work of the
external organs--the organs of motion and of locomotion and the organs of
special sense. These problems are closely related, since they are the two
divisions of the one problem of maintaining life. Neither can be
considered independently of the other. In the chapter following is taken
up the first of these problems.
*Summary.*--The individual parts, or units, that form the body organization
are known as cells. These consist of minute but definitely arranged
portions of protoplasm and are held together by the intercellular
material. They build up the body and carry on its different activities.
The tissues are groups of like cells. By certain general activities the
cells maintain their existence in the tissues and by the exercise of
certain special activities they adapt the tissues to their purposes in the
body. The body, as a cell organization, has its activities directed under
normal conditions toward a single purpose--that of maintaining life. In the
accomplishment of this purpose a nutrient fluid is provided for the cells
and proper relations between the body and its surroundings are
established.
*Exercises.*--1. If a tissue be compared to a brick wall, to what do the
separate bricks correspond? To what the mortar between the bricks?
2. Draw an outline of a typical cell, locating and naming the main
divisions.
3. How do the cells enable the body to grow? Describe the process of
cell-division.
4. How does the general work of cells differ from their special work?
Define absorption, excretion, and assimilation as applied to the cells.
5. Compare the conditions surrounding a one-celled animal, living in
water, to the conditions surrounding the cells in the body.
6. What is meant by the term "environment"? How does man's environment
differ from that of a fish?
7. What is the necessity for a nutrient fluid in the body?
8. Why is the maintenance of life necessarily the chief aim of all the
activities of the body?
9. State the two main problems in the study of the body.
PRACTICAL WORK
*Observations.*--1. Make some scrapings from the inside of the cheek with a
dull knife and mix these with a little water on a glass slide. Place a
cover-glass on the same and examine with a compound microscope. The large
pale cells that can be seen in this way are a variety of epithelial cells.
2. Mount in water on a glass slide some thin slices of cartilage and
examine first with a low and then with a high power of microscope.
(Suitable slices may be cut, with a sharp razor, from the cartilage found
at the end of the rib of a young animal.) Note the small groups of cells
surrounded by, and imbedded in, the intercellular material.
3. Mount and examine with the microscope thin slices of elder pith,
potato, and the stems of growing plants. Make drawings of the cells thus
observed.
4. Examine with the microscope a small piece of the freshly sloughed off
epidermis of a frog's skin. Examine it first in its natural condition, and
then after soaking for an hour or two in a solution of carmine. Make
drawings.
5. Mount on a glass slide some of the scum found on stagnant water and
examine it with a compound microscope. Note the variety and relative size
of the different things moving about. The forms most frequently seen by
such an examination are one-celled plants. Many of these have the power of
motion.
6. Examine tissues of the body, such as nervous, muscular, and glandular
tissues, which have been suitably prepared and mounted for microscopic
study, using low and high powers of the microscope. Make drawings of the
cells in the different tissues thus observed.
CHAPTER IV - THE BLOOD
Two liquids of similar nature are found in the body, known as the blood
and the lymph. These are closely related in function and together they
form the nutrient fluid referred to in the preceding chapter. The blood is
the more familiar of the two liquids, and the one which can best be
considered at this time.
*The Blood: where Found.*--The blood occupies and moves through a system of
closed tubes, known as the blood vessels. By means of these vessels the
blood is made to circulate through all parts of the body, but from them it
does not escape under normal conditions. Though provisions exist whereby
liquid materials may both enter and leave the blood stream, it is only
when the blood vessels are cut or broken that the blood, as blood, is able
to escape from its inclosures.
*Physical Properties of the Blood.*--Experiments such as those described at
the close of this chapter reveal the more important physical properties of
the blood. It may be shown to be heavier and denser than water; to have a
faint odor and a slightly salty taste; to have a bright red color when it
contains oxygen and a dark red color when oxygen is absent; and to
undergo, when exposed to certain conditions, a change called coagulation.
These properties are all accounted for through the different materials
that enter into the formation of the blood.
[Fig. 8]
Fig. 8--Blood corpuscles, highly magnified. _A._ Red corpuscles as they
appear in diluted blood. _B._ Arrangement of red corpuscles in rows
between which are white corpuscles, as may be seen in undiluted blood.
_C._ Red corpuscles much enlarged to show the form.
*Composition of the Blood.*--To the naked eye the blood appears as a thick
but simple liquid; but when examined with a compound microscope, it is
seen to be complex in nature, consisting of at least two distinct
portions. One of these is a clear, transparent liquid; while the other is
made up of many small, round bodies that float in the liquid. The liquid
portion of the blood is called the _plasma_; the small bodies are known as
_corpuscles_. Two varieties of corpuscles are described--the _red_
corpuscles and the _white_ corpuscles (Fig. 8). Other round particles,
smaller than the corpuscles, may also be seen under favorable conditions.
These latter are known as _blood platelets_.
*Red Corpuscles.*--The red corpuscles are classed as cells, although, as
found in the blood of man and the other mammals (Fig. 9), they have no
nuclei.(6) Each one consists of a little mass of protoplasm, called the
_stroma_, which contains a substance having a red color, known as
_hemoglobin_. The shape of the red corpuscle is that of a circular disk
with concave sides. It has a width of about 1/3200 of an inch (7.9
microns(7)) and a thickness of about 1/13000 of an inch (1.9 microns). The
red corpuscles are exceedingly numerous, there being as many as five
millions in a small drop (one cubic millimeter) of healthy blood. But the
number varies somewhat and is greatly diminished during certain forms of
disease.
[Fig. 9]
Fig. 9--Red corpuscles from various animals. Those from mammals are without
nuclei, while those from birds and cold-blooded animals have nuclei.
It is the _function_ of the red corpuscles to serve as _oxygen carriers_
for the cells. They take up oxygen at the lungs and release it at the
cells in the different tissues.(8) The performance of this function
depends upon the hemoglobin.
*Hemoglobin.*--This substance has the remarkable property of forming, under
certain conditions, a weak chemical union with oxygen and, when the
conditions are reversed, of separating from it. It forms about nine tenths
of the solid matter of the red corpuscles and to it is due the colors of
the blood. When united with the oxygen it forms a compound, called
_oxyhemoglobin_, which has a bright red color; the hemoglobin alone has a
dark red color. These colors are the same as those of the blood as it
takes on and gives off oxygen. The stroma, which forms only about one
tenth of the solid matter of the corpuscles, serves as a contrivance for
holding the hemoglobin. The conditions which cause the hemoglobin to unite
with oxygen in the lungs and to separate from it in the tissues, will be
considered later (Chapter VIII).
*Disappearance and Origin of Red Corpuscles.*--The red corpuscles, being
cells without nuclei, are necessarily short-lived. It has been estimated
that during a period of one to two months, all the red corpuscles in the
body at a given time will have disappeared and their places taken by new
ones. The origin of new corpuscles, however, and the manner of ridding the
blood of old ones are problems that are not as yet fully solved. The
removal of the products of broken down corpuscles is supposed to take
place both in the liver and in the spleen.(9)
Regarding the origin of the red corpuscles, the evidence now seems
conclusive that large numbers of them are formed in the red marrow of the
bones. The red marrow is located in what is known as the spongy substance
of the bones (Chapter XIV) and consists, to a large extent, of cells
somewhat like the red corpuscles, but differing from them in having
nuclei. These appear to be constantly in a state of reproduction. The
blood, flowing through the minute cavities containing these cells, carries
those that have been loosened out into the blood stream. Nuclei appear in
the red corpuscles at the time of their formation, but these quickly
separate and, according to some authorities, form the blood platelets.
*White Corpuscles.*--The white corpuscles, or _leucocytes_, are cells of a
general spherical shape, each containing one, two, or more nuclei. They
are much less numerous than the red, there being on the average only one
white corpuscle to about every five hundred of the red ones. On the other
hand, the white corpuscles are larger than the red, one of the former
being equal in volume to about three of the latter.
[Fig. 10]
Fig. 10--*Escape of white corpuscles from a small blood vessel* (Hall). At
_A_ the conditions are normal, but at _B_ some excitation in the
surrounding tissue leads to a migration of corpuscles. 1, 2, and 3 show
different stages of the passage.
The white corpuscles are found, when studied under favorable conditions,
to possess the power of changing their shape and, by this means, of moving
from place to place. This property enables them to penetrate the walls of
capillaries and to pass with the lymph in between the cells of the
tissues. The white corpuscles are, therefore, not confined to the blood
vessels, as are the red corpuscles, but migrate through the intercellular
spaces (Fig. 10). If any part of the body becomes inflamed, the white
corpuscles collect there in large numbers; and, on breaking down, they
form most of the white portion of the sore, called the _pus_.
New white corpuscles are formed from old ones, by cell-division. Their
production may occur in almost any part of the body, but usually takes
place in the lymphatic glands (Chapter VI) and in the spleen, where
conditions for their development are especially favorable. In these places
they are found in great abundance and in various stages of development.
*Functions of White Corpuscles.*--The main use of the white corpuscles
appears to be that of a destroyer of disease germs. These consist of
minute organisms that find their way into the body and, by living upon the
tissues and fluids and by depositing toxins (poisons) in them, cause
different forms of disease. Besides destroying germs that may be present
in the blood, the white corpuscles also leave the blood and attack germs
that have invaded the cells. By forming a kind of wall around any foreign
substance, such as a splinter, that has penetrated the skin, they are able
to prevent the spread of germs through the body. In a similar manner they
also prevent the germs from boils, abscesses, and sore places in general
from getting to and infecting other parts of the body.(10) Another
function ascribed to the white corpuscles is that of aiding in the
coagulation of the blood (page 31); and still another, of aiding in the
healing of wounds.
*Plasma.*--The plasma is a complex liquid, being made up of water and of
substances dissolved in the water. The dissolved substances consist mainly
of foods for the cells and wastes from the cells.
1. _The foods_ represent the same classes of materials as are taken in the
daily fare, _i.e._, proteids, carbohydrates, fats, and salts (Chapter IX).
Three kinds of proteids are found in the plasma, called _serum albumin_,
_serum globulin_, and _fibrinogen_. These resemble, in a general way, the
white of raw egg, but differ from each other in the readiness with which
they coagulate. Fibrinogen coagulates more readily than the others and is
the only one that changes in the ordinary coagulation of the blood. The
others remain dissolved during this process, but are coagulated by
chemical agents and by heat. While all of the proteids probably serve as
food for the cells, the fibrinogen, in addition, is a necessary factor in
the coagulation of the blood (page 31).
The only representative of the carbohydrates in the plasma is _dextrose_.
This is a variety of sugar, being derived from starch and the different
sugars that are eaten. The _fat_ in the plasma is in minute quantities and
appears as fine droplets--the form in which it is found in milk. While
several mineral salts are present in small quantities in the plasma,
_sodium chloride_, or common salt, is the only one found in any
considerable amount. The mineral salts serve various purposes, one of
which is to cause the proteids to dissolve in the plasma.
2. _The wastes_ are formed at the cells, whence they are passed by the
lymph into the blood plasma. They are carried by the blood until removed
by the organs of excretion. The two waste products found in greatest
abundance in the plasma are carbon dioxide and urea.
The substances dissolved in the plasma form about 10 per cent of the whole
amount. The remaining 90 per cent is water. Practically all the
constituents of the plasma, except the wastes, enter the blood from the
digestive organs.
*Purposes of Water in the Blood.*--Not only is water the most abundant
constituent of the blood; it is, in some respects, the most important. It
is the liquefying portion of the blood, holding in solution the
constituents of the plasma and floating the corpuscles. Deprived of its
water, the blood becomes a solid substance. Through the movements of the
blood the water also serves the purpose of a transporting agent in the
body. The cells in all parts of the body require water and this is
supplied to them from the blood. Water is present in the corpuscles as
well as in the plasma and forms about 80 per cent of the entire volume of
the blood.
*Coagulation of the Blood.*--If the blood is exposed to some unnatural
condition, such as occurs when it escapes from the blood vessels, it
undergoes a peculiar change known as _coagulation_.(11) In this change the
corpuscles are collected into a solid mass, known as the _clot_, thereby
separating from a liquid called the _serum_. The serum, which is similar
in appearance to the blood plasma, differs from that liquid in one
important respect as explained below.
*Causes of Coagulation.*--Although coagulation affects all parts of the
blood, only one of its constituents is found in reality to coagulate. This
is the fibrinogen. The formation of the clot and the separation of the
serum is due almost entirely to the action of this substance. Fibrinogen
is for this reason called the _coagulable constituent of the blood_. In
the plasma the fibrinogen is in a liquid form; but during coagulation it
changes into a white, stringy solid, called _fibrin_. This appears in the
clot and is the cause of its formation. Forming as a network of
exceedingly fine and very delicate threads (Fig. 11) _throughout the mass
of blood_ that is coagulating, the fibrin first entangles the corpuscles
and then, by contracting, draws them into the solid mass or clot.(12) The
contracting of the fibrin also squeezes out the serum. This liquid
contains all the constituents of the plasma except the fibrinogen.
[Fig. 11]
Fig. 11--*Fibrin threads* (after Ranvier). These by contracting draw the
corpuscles together and form the clot.
*Fibrin Ferment and Calcium.*--Most difficult of all to answer have been
the questions: What causes the blood to coagulate outside of the blood
vessels and what prevents its coagulation inside of these vessels? The
best explanation offered as yet upon this point is as follows: Fibrinogen
does not of itself change into fibrin, but is made to undergo this change
by the presence of another substance, called _fibrin ferment_. This
substance is not a regular constituent of the blood, but is formed as
occasion requires. It is supposed to result from the breaking down of the
white corpuscles, and perhaps also from the blood platelets, when the
blood is exposed to unnatural conditions. The formation of the ferment
leads in turn to the changing of the fibrinogen into fibrin.
Another substance which is necessary to the process of coagulation is the
element calcium. If compounds of calcium are absent from the blood,
coagulation does not take place. These are, however, regular constituents
of healthy blood. Whether the presence of the calcium is necessary to the
formation of the ferment or to the action of the ferment upon the
fibrinogen is unknown.
*Purpose of Coagulation.*--The purpose of coagulation is to check the flow
of blood from wounds. The fact that the blood is contained in and kept
flowing continuously through a system of _connected_ vessels causes it to
escape rapidly from the body whenever openings in these vessels are made.
Clots form at such openings and close them up, stopping in this way the
flow that would otherwise go on indefinitely. Coagulation, however, does
not stop the flow of blood from the large vessels. From these the blood
runs with too great force for the clot to form within the wound.
*Time Required for Coagulation.*--The rate at which coagulation takes place
varies greatly under different conditions. It is influenced strongly by
temperature; heat hastens and cold retards the process. It may be
prevented entirely by lowering the temperature of the blood to near the
freezing point. The presence of a foreign substance increases the rapidity
of coagulation, and it has been observed that bleeding from small wounds
is more quickly checked by covering them with linen or cotton fibers. The
fibers in this case hasten the process of coagulation.
*Quantity of Blood.*--The quantity of blood is estimated to be about one
thirteenth of the entire weight of the body. This for the average
individual is an amount weighing nearly twelve pounds and having a volume
of nearly one and one half gallons. About 46 per cent by volume of this
amount is made up of corpuscles and 54 per cent of plasma. Of the plasma
about 10 per cent consists of solids and 90 per cent of water, as already
stated.
*Functions of the Blood.*--The blood is the great carrying, or
distributing, agent in the body. Through its movements (considered in the
next chapter) it carries food and oxygen to the cells and waste materials
from the cells. Much of the blood may, therefore, be regarded as _freight_
in the process of transportation. The blood also carries, or distributes,
heat. Taking up heat in the warm parts of the body, it gives it off at
places having a lower temperature. This enables all parts of the body to
keep at about the same temperature.
In addition to serving as a carrier, the blood has antiseptic properties,
i.e., it destroys disease germs. While this function is mainly due to the
white corpuscles, it is due in part to the plasma.(13) Through its
coagulation, the blood also closes leaks in the small blood vessels. The
blood is thus seen to be a liquid of several functions.
[Fig. 12]
Fig. 12--*A balanced change* in water. The level remains constant although
the water is continually changing; suggestive of the changes in the blood.
*Changes in the Blood.*--In performing its functions in the body the blood
must of necessity undergo rapid and continuous change. The red corpuscles,
whose changes have already been noted, appear to be the most enduring
constituents of the blood. The plasma is the portion that changes most
rapidly. Yet in spite of these changes the quantity and character of the
blood remain practically constant.(14) This is because there is a
_balancing_ of the forces that bring about the changes. The addition of
various materials to the blood just equals the withdrawal of the same
materials from the blood. Somewhat as a vessel of water (Fig. 12) having
an inflow and an outflow which are equal in amount may keep always at the
same level, the balancing of the intake and outgo of the blood keeps its
composition about the same from time to time.
*Hygiene of the Blood.*--The blood, being a changeable liquid, is easily
affected through our habits of living. Since it may be affected for ill as
well as for good, one should cultivate those habits that are beneficial
and avoid those that are harmful in their effects. Most of the hygiene of
the blood, however, is properly included in the hygiene of the organs that
act upon the blood--a fact which makes it unnecessary to treat this subject
fully at this time.
From a health standpoint, the most important constituents of the blood
are, perhaps, the corpuscles. These are usually sufficient in number and
vigor in the blood of those who take plenty of physical exercise, accustom
themselves to outdoor air and sunlight, sleep sufficiently, and avoid the
use of injurious drugs. On the other hand, they are deficient in quantity
and inferior in quality in the bodies of those who pursue an opposite
course. Impurities not infrequently find their way into the blood through
the digestive organs. One should eat wholesome, well-cooked food, drink
freely of _pure_ water, and limit the quantity of food _to what can be
properly digested_. The natural purifiers of the blood are the organs of
excretion. The skin is one of these and its power to throw off impurities
depends upon its being clean and active.
*Effect of Drugs.*--Certain drugs and medicines, including alcohol and
quinine,(15) have recently been shown to destroy the white corpuscles. The
effect of such substances, if introduced in considerable amount in the
body, is to render one less able to withstand attacks of disease. Many
patent medicines are widely advertised for purifying the blood. While
these may possibly do good in particular cases, the habit of doctoring
one's self with them is open to serious objection. Instead of taking drugs
and patent medicines for purifying the blood, one should study to live
more hygienically. We may safely rely upon wholesome food, pure water,
outdoor exercise and sunlight, plenty of sleep, and a clean skin for
keeping the blood in good condition. If these natural remedies fail, a
physician should be consulted.
*Summary.*--The blood is the carrying or transporting agent of the body. It
consists in part of constituents, such as the red corpuscles, that enable
it to carry different substances; and in part of the materials that are
being carried. The latter, which include food and oxygen for the cells and
wastes from the cells, may be classed as freight. Certain constituents in
the blood destroy disease germs, and other constituents, by coagulating,
close small leaks in the blood vessels. Although subject to rapid and
continuous change, the blood is able--by reason of the balancing of
materials added to and withdrawn from it--to remain about the same in
quantity and composition.
Exercises.--1. Compare blood and water with reference to weight, density,
color, odor, and complexity of composition.
2. Show by an outline the different constituents of the blood.
3. Compare the red and white corpuscles with reference to size, shape,
number, origin, and function.
4. Name some use or purpose for each constituent of the blood.
5. What constituents of the blood may be regarded as freight and what as
agents for carrying this freight?
6. After coagulation, what portions of the blood are found in the clot?
What portions are found in the serum?
7. What purposes are served by water in the blood?
8. Show how the blood, though constantly changing, is kept about the same
in quantity, density, and composition.
9. In the lungs the blood changes from a dark to a bright red color and in
the tissues it changes back to dark red. What is the cause of these
changes?
10. If the oxygen and hemoglobin formed a strong instead of a weak
chemical union, could the hemoglobin then act as an oxygen carrier? Why?
11. What habits of living favor the development of corpuscles in the
blood?
12. Why will keeping the skin clean and active improve the quality of
one's blood?
PRACTICAL WORK
*To demonstrate the Physical Properties of Blood* (Optional).--Since blood
is needed in considerable quantity in the following experiments, it is
best obtained from the butcher. To be sure of securing the blood in the
manner desired, take to the butcher three good-sized bottles bearing
labels as follows:
*1* Fill two thirds full. While the blood is cooling, stir rapidly with
the hand or a bunch of switches to remove the clot.
*2* Fill two thirds full and set aside without shaking or stirring.
*3* Fill two thirds full and thoroughly mix with the liquid in the bottle.
Label 3 must be pasted on a bottle, having a tight-fitting stopper, which
is filled one fifth full of a saturated solution of Epsom salts. The
purpose of the salts is to prevent coagulation until the blood is diluted
with water as in the experiments which follow.
*Experiments.*--1. Let some of the defibrinated blood (bottle 1) flow (not
fall) on the surface of water in a glass vessel. Does it remain on the
surface or sink to the bottom? What does the experiment show with
reference to the relative weight of blood and water?
2. Fill a large test tube or a small bottle one fourth full of the
defibrinated blood and thin it by adding an equal amount of water. Then
place the hand over the mouth and shake until the blood is thoroughly
mixed with the air. Compare with a portion of the blood not mixed with the
air, noting any difference in color. What substance in the air has acted
on the blood to change its color?
3. Fill three tumblers each two thirds full of water and set them in a
warm place. Pour into one of the tumblers, and thoroughly mix with the
water, two tablespoonfuls of the blood containing the Epsom salts. After
an interval of half an hour add blood to the second tumbler in the same
manner, and after another half hour add blood to the third. The water
dilutes the salts so that coagulation is no longer prevented. Jar the
vessel occasionally as coagulation proceeds; and if the clot is slow in
forming, add a trace of some salt of calcium (calcium chloride). After the
blood has been added to the last tumbler make a comparative study of all.
Note that coagulation begins in all parts of the liquid at the same time
and that, as the process goes on, the clot shrinks and is drawn toward the
center.
4. Place a clot from one of the tumblers in experiment 3 in a large vessel
of water. Thoroughly wash, adding fresh water, until a white, stringy
solid remains. This substance is fibrin.
5. Examine the coagulated blood obtained from the butcher (bottle 2).
Observe the dark central mass (the clot) surrounded by a clear liquid (the
serum). Sketch the vessel and its contents, showing and naming the parts
into which the blood separates by coagulation.
*To examine the Red Corpuscles.*--Blood for this purpose is easily obtained
from the finger. With a handkerchief, wrap one of the fingers of the left
hand from the knuckle down to the first joint. Bend this joint and give it
a sharp prick with the point of a sterilized 'needle just above the root
of the nail. Pressure applied to the under side of the finger will force
plenty of blood through a very small opening. (To prevent any possibility
of blood poisoning the needle should be sterilized. This may be done by
dipping it in alcohol or by holding it for an instant in a hot flame. It
is well also to wash the finger with soap and water, or with alcohol,
before the operation.) Place a small drop of the blood in the middle of a
glass slide, protect the same with a cover glass, and examine with a
compound microscope. At least two specimens should be examined, one of
which should be diluted with a little saliva or a physiological salt
solution.(16) In the diluted specimen the red corpuscles appear as
amber-colored, circular, disk-shaped bodies. In the undiluted specimen
they show a decided tendency to arrange themselves in rows, resembling
rows of coins. (Singly, the corpuscles do not appear red when highly
magnified.)
A few white corpuscles may generally be found among the red ones in the
undiluted specimen. These become separated by the formation of the red
corpuscles into rows. They are easily recognized by their larger size and
by their silvery appearance, due to the light shining through them.
*To examine White Corpuscles.*--Obtain from the butcher a small piece of
the neck sweetbread of a calf. Press it between the fingers to squeeze out
a whitish, semi-liquid substance. Dilute with physiological salt solution
on a glass slide and examine with a compound microscope. Numerous white
corpuscles of different kinds and sizes will be found. Make sketches.
*To prepare Models of Red Corpuscles.*--Several models of red corpuscles
should be prepared for the use of the class. Clay and putty may be pressed
into the form of red corpuscles and allowed to harden, and small models
may be cut out of blackboard crayon. Excellent models can be molded from
plaster of Paris as follows: Coat the inside of the lid of a baking powder
can with oil or vaseline and fill it even full of a thick mixture of
plaster of Paris and water. After the plaster has set, remove it from the
lid and with a pocket-knife round off the edges and hollow out the sides
until the general form of the corpuscle is obtained. The models may be
colored red if it is desired to match the color as well as the form of the
corpuscle.
CHAPTER V - THE CIRCULATION
A Carrier must move. To enable the blood to carry food and oxygen _to_ the
cells and waste materials _from_ the cells, and also to distribute heat,
it is necessary to keep it moving, or circulating, in all parts of the
body. So closely related to the welfare of the body is the circulation(17)
of the blood, that its stoppage for only a brief interval of time results
in death.
*Discovery of the Circulation.*--The discovery of the circulation of the
blood was made about 1616 by an English physician named Harvey. In 1619 he
announced it in his public lectures and in 1628 he published a treatise in
Latin on the circulation. The chief arguments advanced in support of his
views were the presence of valves in the heart and veins, the continuous
movement of the blood in the same direction through the blood vessels, and
the fact that the blood comes from a cut artery in jets, or spurts, that
correspond to the contractions of the heart.
No other single discovery with reference to the human body has proved of
such great importance. A knowledge of the nature and purpose of the
circulation was the necessary first step in understanding the plan of the
body and the method of maintaining life, and physiology as a science dates
from the time of Harvey's discovery.
*Organs of Circulation.*--The organs of circulation, or blood vessels, are
of four kinds, named the heart, the arteries, the capillaries, and the
veins. They serve as contrivances both for holding the blood and for
keeping it in motion through the body. The heart, which is the chief organ
for propelling the blood, acts as a force pump, while the arteries and
veins serve as tubes for conveying the blood from place to place.
Moreover, the blood vessels are so connected that the blood moves through
them in a regular order, performing two well-defined circuits.
[Fig. 13]
Fig. 13--*Heart* in position in thoracic cavity. Dotted lines show positin
of diaphragm and of margins of lungs.
*The Heart.*--The human heart, roughly speaking, is about the size of the
clenched fist of the individual owner. It is situated very near the center
of the thoracic cavity and is almost completely surrounded by the lungs.
It is cone-shaped and is so suspended that the small end hangs downward,
forward, and a little to the left. When from excitement, or other cause,
one becomes conscious of the movements of the heart, these appear to be in
the left portion of the chest, a fact which accounts for the erroneous
impression that the heart is on the left side. The position of the heart
in the cavity of the chest is shown in Fig. 13.
*The Pericardium.*--Surrounding the heart is a protective covering, called
the pericardium. This consists of a closed membranous sac so arranged as
to form a double covering around the heart. The heart does not lie inside
of the pericardial sac, as seems at first glance to be the case, but its
relation to this space is like that of the hand to the inside of an empty
sack which is laid around it (Fig. 14). The inner layer of the pericardium
is closely attached to the heart muscle, forming for it an outside
covering. The outer layer hangs loosely around the heart and is continuous
with the inner layer at the top. The outer layer also connects at certain
places with the membranes surrounding the lungs and is attached below to
the diaphragm. Between the two layers of the pericardium is secreted a
liquid which prevents friction from the movements of the heart.
[Fig. 14]
Fig. 14--*Diagram of section of the pericardial sac*, heart removed. _A._
Place occupied by the heart. _B._ Space inside of pericardial sac. _a._
Inner layer of pericardium and outer lining of heart. _b._ Outer layer of
pericardium. _C._ Covering of lung. _D._ Diaphragm.
*Cavities of the Heart.*--The heart is a hollow, muscular organ which has
its interior divided by partitions into four distinct cavities. The main
partition extends from top to bottom and divides the heart into two
similar portions, named from their positions the right side and the left
side. On each side are two cavities, the one being directly above the
other. The upper cavities are called _auricles_ and the lower ones
_ventricles_. To distinguish these cavities further, they are named from
their positions the right auricle and the left auricle, and the right
ventricle and the left ventricle (Fig. 15). The auricles on each side
communicate with the ventricles below; but after birth there is no
communication between the cavities on the opposite sides of the heart. All
the cavities of the heart are lined with a smooth, delicate membrane,
called the _endocardium_.
[Fig. 15]
Fig. 15--*Diagram showing plan of the heart.* 1. Semilunar valves. 2.
Tricuspid valve. 3. Mitral valve. 4. Right auricle. 5. Left auricle. 6.
Right ventricle. 7. Left ventricle. 8. Chordae tendineae. 9. Inferior vena
cava. 10. Superior vena cava. 11. Pulmonary artery. 12. Aorta. 13.
Pulmonary veins.
*Valves of the Heart.*--Located at suitable places in the heart are four
gate-like contrivances, called valves. The purpose of these is _to give
the blood a definite direction_ in its movements. They consist of tough,
inelastic sheets of connective tissue, and are so placed that pressure on
one side causes them to come together and shut up the passageway, while
pressure on the opposite side causes them to open. A valve is found at the
opening of each auricle into the ventricle, and at the opening of each
ventricle into the artery with which it is connected.
The valve between the right auricle and the right ventricle is called the
_tricuspid_ valve. It is suspended from a thin ring of connective tissue
which surrounds the opening, and its free margins extend into the
ventricle (Fig. 16). It consists of three parts, as its name implies,
which are thrown together in closing the opening. Joined to the free edges
of this valve are many small, tendinous cords which connect at their lower
ends with muscular pillars in the walls of the ventricle. These are known
as the _chordae tendineae_, or heart tendons. Their purpose is to serve as
_valve stops_, to prevent the valve from being thrown, by the force of the
blood stream, back into the auricle.
The _mitral_, or bicuspid, valve is suspended around the opening between
the left auricle and the left ventricle, with the free margins extending
into the ventricle. It is exactly similar in structure and arrangement to
the tricuspid valve, except that it is stronger and is composed of two
parts instead of three.
[Fig. 16]
Fig. 16--*Right side of heart* dissected to show cavities and valves. _B._
Right semilunar valve. The tricuspid valve and the chordae tendineae shown
in the ventricle.
The _right semilunar_ valve is situated around the opening of the right
ventricle into the pulmonary artery. It consists of three pocket-shaped
strips of connective tissue which hang loosely from the walls when there
is no pressure from above; but upon receiving pressure, the pockets fill
and project into the opening, closing it completely (Fig. 16). The _left
semilunar_ valve is around the opening of the left ventricle into the
aorta, and is similar in all respects to the right semilunar valve.
*Differences in the Parts of the Heart.*--Marked differences are found in
the walls surrounding the different cavities of the heart. The walls of
the ventricles are much thicker and stronger than those of the auricles,
while the walls of the left ventricle are two or three times thicker than
those of the right. A less marked but similar difference exists between
the auricles and also between the valves on the two sides of the heart.
These differences in structure are all accounted for by the work done by
the different portions of the heart. The greater the work, the heavier the
structures that perform the work.
[Fig. 17]
Fig. 17--*Diagram of the circulation*, showing in general the work done by
each part of the heart. The right ventricle forces the blood through the
lungs and into the left auricle. The left ventricle forces blood through
all parts of the body and back to the auricle. The auricles force blood
into the ventricles.
*Connection with Arteries and Veins.*--Though the heart is in communication
with all parts of the circulatory system, it makes actual connection with
only a few of the blood tubes. These enter the heart at its upper portion
(Fig. 15), but connect with its different cavities as follows:
1. _With the right auricle_, the superior and the inferior venae cavae and
the coronary veins. The superior vena cava receives blood from the head
and the upper extremities; the inferior vena cava, from the trunk and the
lower extremities; and the coronary veins, from the heart itself.
2. _With the left auricle_, the four pulmonary veins. These receive blood
from the lungs and empty it into the left auricle.
3. _With the right ventricle_, the pulmonary artery. This receives blood
from the heart and by its branches distributes it to all parts of the
lungs.
4. _With the left ventricle_, the aorta. The aorta receives blood from the
heart and through its branches delivers it to all parts of the body.
*How the Heart does its Work.*--The heart is a muscular pump(18) and does
its work through the contracting and relaxing of its walls. During
contraction the cavities are closed and the blood is forced out of them.
During relaxation the cavities open and are refilled. The valves direct
the flow of the blood, being so arranged as to keep it moving always in
the same direction (Fig. 17).
The heart, however, is not a single or a simple pump, but consists in
reality of _four_ pumps which correspond to its different cavities. These
connect with each other and with the blood vessels over the body in such a
manner that each aids in the general movement of the blood.
[Fig. 18]
Fig. 18--Diagram illustrating the "cardiac cycle."
*Work of Auricles and Ventricles Compared.*--In the work of the heart the
two auricles contract at the same time--their contraction being followed
immediately by the contraction of both ventricles. After the contraction
of the ventricles comes a period of rest, or relaxation, about equal in
time to the period of contraction of both the auricles and the
ventricles.(19) On account of the work which they perform, the auricles
have been called the "feed pumps" of the heart; and the ventricles, the
"force pumps."(20) It is the function of the auricles to collect the blood
from the veins, to let this run slowly into the ventricles when both the
auricles and ventricles are relaxed, and finally, by contracting, _to
force an excess of blood into the ventricles_, thereby distending their
walls. The ventricles, having in this way been fully charged by the
auricles, now contract and force their contents into the large arteries.
*Sounds of the Heart.*--Two distinct sounds are given out by the heart as
it pumps the blood. One of them is a dull and rather heavy sound, while
the other is a short, sharp sound. The short sound follows quickly after
the dull sound and the two are fairly imitated by the words "lubb, dup."
While the cause of the first sound is not fully understood, most
authorities believe it to be due to the contraction of the heart muscle
and the sudden tension on the valve flaps. The second sound is due to the
closing of the semilunar valves. These sounds are easily heard by placing
an ear against the chest wall. They are of great value to the physician in
determining the condition of the heart.
*Arteries and Veins.*--These form two systems of tubes which reach from the
heart to all parts of the body. The arteries receive blood from the heart
and distribute it to the capillaries. The veins receive the blood from the
capillaries and return it to the heart. The arteries and veins are similar
in structure, both having the form of tubes and both having three distinct
layers, or coats, in their walls. The corresponding coats in the arteries
and veins are made up of similar materials, as follows:
1. _The inner coat_ consists of a delicate lining of flat cells resting
upon a thin layer of connective tissue. The inner coat is continuous with
the lining of the heart and provides a smooth surface over which the blood
glides with little friction.
2. _The middle coat_ consists mainly of non-striated, or involuntary,
muscular fibers. This coat is quite thin in the veins, but in the arteries
it is rather thick and strong.
3. _The outer coat_ is made up of a variety of connective tissue and is
also much thicker and stronger in the arteries than in the veins.
[Fig. 19]
Fig. 19--Artery dissected to show the coats.
Marked differences exist between the arteries and the veins, and these
vessels are readily distinguished from each other. The walls of the
arteries are much thicker and heavier than those of the veins (Fig. 19).
As a result these tubes stand open when empty, whereas the veins collapse.
The arteries also are highly elastic, while the veins are but slightly
elastic. On the other hand, many of the veins contain valves, formed by
folds in the inner coat (Fig. 20), while the arteries have no valves. The
blood flows more rapidly through the arteries than through the veins, the
difference being due to the fact that the system of veins has a greater
capacity than the system of arteries.
[Fig. 20]
Fig. 20--Vein split open to show the valves.
*Why the Arteries are Elastic.*--The elasticity of the arteries serves a
twofold purpose. It keeps the arteries from bursting when the blood is
forced into them from the ventricles, and it is a means of _supplying
pressure to the blood while the ventricles are in a condition of
relaxation._ The latter purpose is accomplished as follows:
Contraction of the ventricles fills the arteries overfull, causing them to
swell out and make room for the excess of blood. Then while the ventricles
are resting and filling, the stretched arteries press upon the blood to
keep it flowing into the capillaries. In this way _they cause the
intermittent flow from, the heart to become a steady stream in the
capillaries_.
The swelling of the arteries at each contraction of the ventricle is
easily felt at certain places in the body, such as the wrist. This
expansion, known as the "pulse," is the chief means employed by the
physician in determining the force and rapidity of the heart's action.
*Purpose of the Valves in the Veins.*--The valves in the veins are not used
for directing the _general_ flow of the blood, the valves of the heart
being sufficient for this purpose. Their presence is necessary because of
the pressure to which the veins are subjected in different parts of the
body. The contraction of a muscle will, for example, close the small veins
in its vicinity and diminish the capacity of the larger ones. The natural
tendency of such pressure is to empty the veins in two directions--one in
the same direction as the regular movement of the blood, but the other in
the opposite direction. The valves by closing cause the contracting muscle
to push the blood in one direction only--toward the heart. The valves in
the veins are, therefore, an economical device for _enabling variable
pressure_ in different parts of the body _to assist in the circulation_.
Veins like the inferior vena cava and the veins of the brain, which are
not compressed by movements of the body, do not have valves.
*Purposes of the Muscular Coat.*--The muscular coat, which is thicker in
the arteries than in the veins and is more marked in small arteries than
in large ones, serves two important purposes. In the first place it,
together with the elastic tissue, keeps the capacity of the blood vessels
_equal to the volume of the blood_. Since the blood vessels are capable of
holding more blood than may be present at a given time in the body, there
is a liability of empty spaces occurring in these tubes. Such spaces would
seriously interfere with the circulation, since the heart pressure could
not then reach all parts of the blood stream. This is prevented by the
contracted state, or "tone," of the blood vessels, due to the muscular
coat.
In the second place, the muscular coat serves the purpose of _regulating_
the amount of blood which any given organ or part of the body receives.
This it does by varying the caliber of the arteries going to the organ in
question. To increase the blood supply, the muscular coat relaxes. The
arteries are then dilated by the blood pressure from within so as to let
through a larger quantity of blood. To diminish the supply, the muscle
contracts, making the caliber of the arteries less, so that less blood can
flow to this part of the body. Since the need of organs for blood varies
with their activity, the muscular coat serves in this way a very necessary
purpose.
[Fig. 21]
Fig. 21--Diagram of network of capillaries between a very small artery and
a very small vein. Shading indicates the change of color of the blood as
it passes through the capillaries. _S._ Places between capillaries
occupied by the cells.
*Capillaries.*--The capillaries consist of a network of minute blood
vessels which connect the terminations of the smallest arteries with the
beginnings of the smallest veins (Fig. 21). They have an average diameter
of less than one two-thousandth of an inch (12 mu) and an average length of
less than one twenty-fifth of an inch (1 millimeter). Their walls consist
of a single coat which is continuous with the lining of the arteries and
veins. This coat is formed of a single layer of thin, flat cells placed
edge to edge (Fig. 22). With a few exceptions, the capillaries are found
in great abundance in all parts of the body.
[Fig. 22]
Fig. 22--*Surface of capillary* highly magnified, showing its coat of thin
cells placed edge to edge.
*Functions of the Capillaries.*--On account of the thinness of their walls,
the capillaries are able to serve a twofold purpose in the body:
1. They admit materials into the blood vessels.
2. They allow materials to pass from the blood vessels to the surrounding
tissues.
When it is remembered that the blood, as blood, does not escape from the
blood vessels under normal conditions, the importance of the work of the
capillaries is apparent. To serve its purpose as a carrier, there must be
places where the blood can load up with the materials which it is to
carry, and places also where these can be unloaded. Such places are
supplied by the capillaries.
The capillaries also serve the purpose of spreading the blood out and of
bringing it very near the individual cells in all parts of the body (Fig.
21).
*Functions of Arteries and Veins.*--While the capillaries provide the means
whereby materials may both enter and leave the blood, the arteries and
veins serve the general purpose of passing the blood from one set of
capillaries to another. Since pressure is necessary for moving the blood,
these tubes must connect with the source of the pressure, which is the
heart. In the arteries and veins the blood neither receives nor gives up
material, but having received or given up material at one set of
capillaries, it is then pushed through these tubes to where it can serve a
similar purpose in another set of capillaries (Fig. 23).
*Divisions of the Circulation.*--Man, in common with all warm-blooded
animals, has a double circulation, a fact which explains the double
structure of his heart. The two divisions are known as the _pulmonary_ and
the _systemic_ circulations. By the former the blood passes from the right
ventricle through the lungs, and is then returned to the left auricle; by
the latter it passes from the left ventricle through all parts of the
body, returning to the right auricle.
The general plan of the circulation is indicated in Fig. 23. All the blood
flows continuously through both circulations and passes the various parts
in the following order: right auricle, tricuspid valve, right ventricle,
right semilunar valve, pulmonary artery and its branches, capillaries of
the lungs, pulmonary veins, left auricle, mitral valve, left ventricle,
left semilunar valve, aorta and its branches, systemic capillaries, the
smaller veins, superior and inferior venae cavae, and then again into the
right auricle.
In the pulmonary capillaries the blood gives up carbon dioxide and
receives oxygen, changing from a dark red to a bright red color. In the
systemic capillaries it gives up oxygen, receives carbon dioxide and other
impurities, and changes back to a dark red color.
In addition to the two main divisions of the circulation, special circuits
are found in various places. Such a circuit in the liver is called the
_portal_ circulation, and another in the kidneys is termed the _renal_
circulation. To some extent the blood supply to the walls of the heart is
also outside of the general movement; it is called the _coronary_
circulation.
[Fig. 23]
Fig. 23--*General scheme of the circulation*, showing places where the
blood takes on and gives off materials. 1. Body in general. 2. Lungs. 3.
Kidneys. 4. Liver. 5. Organs of digestion. 6. Lymph ducts. 7. Pulmonary
artery. 8. Aorta.
*Blood Pressure and Velocity.*--The blood, in obedience to physical laws,
passes continuously through the blood vessels, moving always from a place
of greater to one of less pressure. Through the contraction of the
ventricles, a relatively high pressure is maintained in the arteries
nearest the heart.(21) This pressure diminishes rapidly in the small
arteries, becomes comparatively slight in the capillaries, and falls
practically to nothing in the veins. Near the heart in the superior and
inferior venae cavae, the pressure at intervals is said to be _negative_.
This means that the blood from these veins is actually drawn into the
right auricle by the expansion of the chest walls in breathing.(22)
The velocity of the blood is greatest in the arteries, less in the veins,
and _much_ less in the capillaries than in either the arteries or the
veins. The slower flow of the blood through the capillaries is accounted
for by the fact that their united area is many times greater than that of
the arteries which supply, or the veins which relieve, them. This allows
the same quantity of blood, flowing through them in a given time, a wider
channel and causes it to move more slowly. The time required for a
complete circulation is less than one minute.
*Summary of Causes of Circulation.*--The chief factor in the circulation of
the blood is, of course, the heart. The ventricles keep a pressure on the
blood which is sufficient to force it through all the blood tubes and back
to the auricles. The heart is aided in its work by the elasticity of the
arteries, which keeps the blood under pressure while the ventricles are in
a state of relaxation. It is also aided by the muscles and elastic tissue
in all of the blood vessels. These, by keeping the blood vessels in a
state of "tone," or so contracted that their capacity just equals the
volume of the blood, enable pressure from the heart to be transmitted to
all parts of the blood stream. A further aid to the circulation is found
in the valves in the veins, which enable muscular contraction within the
body, and variable pressure upon its surface, to drive the blood toward
the heart. The heart is also aided to some extent by the movements of the
chest walls in breathing. The organs Of circulation are under the control
of the nervous system (Chapter XVIII).
HYGIENE OF THE CIRCULATION
*Care of the Heart.*--The heart, consisting largely of muscle, is subject
to the laws of muscular exercise. It may be injured by over-exertion, but
is strengthened by a moderate increase in its usual work.(23) It may even
be subjected to great exertion without danger, if it be trained by
gradually increasing its work. Such training, by giving the heart time to
gain in size and strength, prepares it for tasks that could not at first
be accomplished.
In taking up a new exercise requiring considerable exertion, precautions
should be observed to prevent an overstrain of the heart. The heart of the
amateur athlete, bicyclist, or mountain climber is frequently injured by
attempting more than the previous training warrants. The new work should
be taken up gradually, and feats requiring a large outlay of physical
energy should be attempted only after long periods of training.
Since the heart is controlled by the nervous system, it frequently becomes
irregular in its action through conditions that exhaust the nervous
energy. Palpitations of the heart, the missing of beats, and pains in the
heart region frequently arise from this cause. It is through their effect
upon the nervous system that worry, overstudy, undue excitement, and
dissipation cause disturbances of the heart. In all such cases the remedy
lies in the removal of the cause. The nervous system should also be "toned
up" through rest, plenty of sleep, and moderate exercise in the open air.
*Effect of Drugs.*--A number of substances classed as drugs, mainly by
their action on the nervous system, produce undesirable effects upon the
organs of circulation. Unfortunately some of these are extensively used,
alcohol being one of them. If taken in any but small quantities, alcohol
is a disturbing factor in the circulation. It increases the rate of the
heart beat and dilates the capillaries. Its effect upon the capillaries is
shown by the "bloodshot" eye and the "red nose" of the hard drinker.
Another bad effect from the use of much alcohol is the weakening of the
heart through the accumulation of fat around this organ and within the
heart muscle. The use of alcohol also leads in many cases to a hardening
of the walls of the arteries, such as occurs in old age. This effect makes
the use of alcohol especially dangerous for those in advanced years.
Tobacco contains a drug, called nicotine, which has a bad effect upon the
heart in at least two ways: 1. When the use of tobacco is begun in early
life, it interferes with the growth of the heart, leading to its weakness
in the adult. 2. When used in considerable quantity, by young or old, it
causes a nervous condition both distressing and dangerous, known as
"tobacco heart."
Tea and coffee contain a drug, called caffeine, which acts upon the
nervous system and which may, on this account, interfere with the proper
control of the heart. In some individuals the taking of a very small
amount of either tea or coffee is sufficient to cause irregularities in
the action of the heart. Tea is considered the milder of the two liquids
and the one less liable to injure.
*Effect of Rheumatism.*--The disease which affects the heart more
frequently than any other is rheumatism. This attacks the lining membrane,
or endocardium, and causes, not infrequently, a shrinkage of the heart
valves. The heart is thus rendered defective and, to perform its function
in the body, must work harder than if it were in a normal condition.
Rheumatic attacks of the heart do most harm when they occur in early
life--the period when the valves are the most easily affected. Any tendency
toward rheumatism in children has, therefore, a serious significance and
should receive the attention of the physician. Any one having a defective
heart should avoid all forms of exercise that demand great exertion.
*Strengthening of the Blood Vessels.*--Disturbances of the circulation,
causing too much blood to be sent to certain parts of the body and an
insufficient amount to others, when resulting from slight causes, are
usually due to weakness of the walls of the blood vessels, particularly of
the muscular coat. Such weakness is frequently indicated by extreme
sensitiveness to heat or cold and by a tendency to "catch cold." From a
health standpoint the preservation of the normal muscular "tone" of the
blood vessels is a problem of great importance. Though the muscles of the
blood vessels cannot be exercised in the same manner as the voluntary
muscles, they may be called actively into play through all the conditions
that induce changes in the blood supply to different parts of the body.
The usual forms of physical exercise necessitate such changes and
indirectly exercise the muscular coat. The exposure of the body to cold
for short intervals, because of the changes in the circulation which this
induces, also serves the same purpose. A cold bath taken with proper
precautions is beneficial to the circulation of many and so also is a
brisk walk on a frosty morning. Both indirectly exercise and strengthen
the muscular coat of the blood vessels. On the other hand, too much time
spent indoors, especially in overheated rooms, leads to a weakening of the
muscular coat and should be avoided.
*Checking of Flow of Blood from Wounds.*--The loss of any considerable
quantity of blood is such a serious matter that every one should know the
simpler methods of checking its flow from wounds. In small wounds the flow
is easily checked by binding cotton or linen fiber over the place. The
absorbent cotton, sold in small packages at drug stores, is excellent for
this purpose and should be kept in every home. A simple method of checking
"nosebleed" is that of drawing air through the bleeding nostril, while the
other nostril is compressed with the finger.(24) Another method is to
"press with the finger (or insert a small roll of paper) under the lip
against the base of the nose." (25) Where the bleeding is persistent, the
nostril should be plugged with a small roll of clean cotton or paper. When
this is done, the plug should not be removed too soon because of the
likelihood of starting the flow afresh.
In dealing with large wounds the services of a physician are
indispensable. But in waiting for the physician to arrive temporary aid
must be rendered. The one who gives such aid should first decide whether
an artery or a vein has been injured. This is easily determined by the
nature of the blood stream, which is in jets, or spurts, from an artery,
but flows steadily from a vein. If an artery is injured, the limb should
be tightly bandaged on the side of the wound nearest the heart; if a vein,
on the side farthest from the heart. In addition to this, the edges of the
wound should be closed and covered with cotton fiber and the limb should
be placed on a support above the level of the rest of the body. A large
handkerchief makes a convenient bandage if properly applied. This should
be folded diagonally and a knot tied in the middle. Opposite ends are then
tied, making a loose-fitting loop around the limb. The knot is placed
directly over the blood vessel to be compressed and a short stick inserted
in the loop. The necessary pressure is then applied by twisting the
handkerchief with the stick. Time must not be lost, however, in the
preparation of a suitable bandage. The blood vessel should be compressed
with the fingers while the bandage is being prepared.
*Summary.*--The blood, to serve as a transporting agent, must be kept
continually moving through all parts of the body. The blood vessels hold
the blood, supply the channels and force necessary for its circulation,
and provide conditions which enable materials both to enter and to leave
the blood stream. The heart is the chief factor in propelling the blood,
although the muscles and the elastic tissue in the walls of the arteries
and the valves in the veins are necessary aids in the process. In the
capillaries the blood takes on and gives off materials, while the arteries
and veins serve chiefly as tubes for conveying the blood from one system
of capillaries to another.
*Exercises.*--1. Of what special value in the study of the body was the
discovery of the circulation of the blood?
2. State the necessity for a circulating liquid in the body.
3. Show by a drawing the general plan of the heart, locating and naming
the essential parts. Show also the connection of the large blood vessels
with the cavities of the heart.
4. Compare the purpose served by the chordae tendineae to that served by
doorstops (the strips against which the door strikes in closing).
5. Explain how the heart propels the blood. To what class of pumps does it
belong? What special work is performed by each of its divisions?
6. Define a valve. Of what use are the valves in the heart? In the veins?
7. By what means is pressure from contracting muscles in different parts
of the body made to assist in the circulation?
8. Of what advantage is the elasticity of the arteries?
9. How is blood forced from the capillaries back to the heart?
10. Why should there be a difference in structure between the two sides of
the heart?
11. Following Fig. 23, trace the blood through a complete circulation,
naming all the divisions of the system in the order of the flow of the
blood.
12. If the period of rest following the period of contraction of the heart
be as long as the period of contraction, how many hours is the heart able
to rest out of every twenty-four?
13. State the functions of the capillaries. Show how their structure
adapts them to their work.
14. What kind of physical exercise tends to strengthen the heart? What
forms of exercise tend to injure it? State the effects of alcohol and
tobacco on the heart.
15. How may rheumatism injure the heart?
16. Give directions for checking the flow of blood from small and from
large blood vessels.
PRACTICAL WORK
In showing the relations of the different parts of the heart, a large
dissectible model is of great service (Fig. 24). Indeed, where the time of
the class is limited, the practical work may be confined to the study of
the heart model, diagrams of the heart and the circulation, and a few
simple experiments. However, where the course is more extended, the
dissection of the heart of some animal as described below is strongly
advised.
*Observations on the Heart.*--Procure, by the assistance of a butcher, the
heart of a sheep, calf, or hog. To insure the specimen against mutilation,
the lungs and the diaphragm must be left attached to the heart. In
studying the different parts, good results will be obtained by observing
the following order:
1. Observe the connection of the heart to the lungs, diaphragm, and large
blood vessels. Inflate the lungs and observe the position of the heart
with reference to them.
2. Examine the sac surrounding the heart, called the _pericardium_. Pierce
its lower portion and collect the pericardial fluid. Increase the opening
thus made until it is large enough to slip the heart out through it. Then
slide back the pericardium until its connection with the large blood
vessels above the heart is found. Observe that a thin layer of it
continues down from this attachment, forming the outer covering of the
heart.
3. Trace out for a short distance and study the veins and arteries
connected with the heart. The arteries are to be distinguished by their
thick walls. The heart may now be severed from the lungs by cutting the
large blood vessels, care being taken to leave a considerable length of
each one attached to the heart.
[Fig. 24]
Fig. 24--Model for demonstrating the heart.
4. Observe the outside of the heart. The thick, lower portion contains the
cavities called _ventricles_; the thin, upper, ear-shaped portions are the
_auricles_. The thicker and denser side lies toward the left of the
animal's body and is called the _left_ side of the heart; the other is the
_right_ side. Locate the right auricle and the right ventricle; the left
auricle and the left ventricle.
5. Lay the heart on the table with the front side up and the apex pointing
from the operator. This places the left side of the heart to his left and
the right side to his right. Notice the groove between the ventricles,
called the inter-ventricular groove. Make an incision half an inch to the
right of this groove and cut toward the base of the heart until the
pulmonary artery is laid open. Then, following within half an inch of the
groove, cut down and around the right side of the heart. The wall of the
right ventricle may now be raised and the cavity exposed. Observe the
extent of the cavity, its shape, its lining, its columns of muscles, its
half columns of muscles, its tendons (chordae tendineae), the tricuspid
valve from the under side, etc. Also notice the valve at the beginning of
the pulmonary artery (the right semilunar) and the sinuses, or
depressions, in the artery immediately behind its divisions.
6. Now cut through the middle of the loosened ventricular wall from the
apex to the middle of the right auricle, laying it open for observation.
Observe the openings into the auricle, there being one each for the vena
cava superior, the vena cava inferior, and the coronary vein. Compare the
walls, lining, shape, size, etc., with the ventricle below.
7. Cut off the end of the left ventricle about an inch above the apex.
This will show the extension of the cavity to the apex; it will also show
the thickness of the walls and the shape of the cavity. Split up the
ventricular wall far enough to examine the mitral valve and the chordae
tendineae from the lower side.
8. Make an incision in the left auricle. Examine its inner surface and
find the places of entrance of the pulmonary veins. Examine the mitral
valve from above. Compare the two sides of the heart, part for part.
9. Separate the aorta from the other blood vessels and cut it entirely
free from the heart, care being taken to leave enough of the heart
attached to the artery to insure the semilunar valve's being left in good
condition. After tying or plugging up the holes in the sides of the
artery, pour water into the small end and observe the closing of the
semilunar valve. Repeat the experiment until the action of the valve is
understood. Sketch the artery, showing the valve in a closed condition.
*To illustrate the Action of a Ventricle.*--Procure a syringe bulb with an
opening at each end. Connect a rubber tube with each opening, letting the
tubes reach into two tumblers containing water. By alternately compressing
and releasing the bulb, water is pumped from one vessel into the other.
The bulb may be taken to represent one of the ventricles. What action of
the ventricle is represented by compressing the bulb? By releasing the
pressure? Show by a sectional drawing the arrangement of the valves in the
syringe bulb.
[Fig. 25]
Fig. 25--Illustrating elasticity of arteries.
*To show the Advantage of the Elasticity of Arteries.*--Connect the syringe
bulb used in the last experiment with a rubber tube three or four feet in
length and having rather thin walls. In the opposite end of the rubber
tube insert a short glass tube which has been drawn (by heating) to a fine
point (Fig. 25). Pump water into the rubber tube, observing:
1. The swelling of the tube (pulse) as the water is forced into it. (This
is best observed by placing the fingers on the tube.)
2. The forcing of water from the pointed tubs during the interval when no
pressure is being applied from the bulb. Compare with the action of the
arteries when blood is forced into them from the ventricles.
Repeat the experiment, using a long glass tube terminating in a point
instead of the rubber tube. (In fitting the glass tube to the bulb use a
very short rubber tube.) Observe and account for the differences in the
flow of water through the inelastic tube.
*To show the Advantage of Valves in the Veins.*--Attach an open glass tube
one foot in length to each end of the rubber tube used in the preceding
experiment and fill with water (by sucking) to within about six inches of
the end. Lay on the table with the glass tubes secured in an upright
position (Fig. 26). Now compress the tube with the hand, noting that the
water rises in both tubes, being pushed in both directions. This effect is
similar to that produced on the blood when a vein having no valves is
compressed.
[Fig. 26]
Fig. 26.--*Simple apparatus* for showing advantage of valves in veins.
Now imitate the action of a valve by clamping the tube at one point, or by
closing it by pressure from the finger, and then compressing with the hand
some portion of the tube on the table. Observe in this instance that the
water is *all* pushed in the same direction. The movement of the water is
now like the effect produced on the blood in veins having valves when the
veins are compressed.
*To show the Position of the Valves in the Veins.*--Exercise the arm and
hand for a moment to increase the blood supply. Expose the forearm and
examine the veins on its surface. With a finger, stroke one of the veins
toward the heart, noting that, as the blood is pushed along on one side of
the finger the blood follows on the other side. Now stroke the vein toward
the hand. Places are found beyond which the blood does not follow the
finger. These mark the positions of valves.
*To show Effect of Exercise upon the Circulation.*--1. With a finger on the
"pulse" at the wrist or temple, count the number of heart beats during a
period of one minute under the following conditions: (_a_) when sitting;
(_b_) when standing; (_c_) after active exercise, as running. What
relation, if any, do these observations indicate between the general
activity of the body and the work of the heart?
2. Compare the size of the veins on the backs of the hands when they are
placed side by side on a table. Then exercise briskly the right hand and
arm, clenching and unclenching the fist and flexing the arm at the elbow.
Place the hands again side by side and, after waiting a minute, observe
the increase in the size of the veins in the hand exercised. How is this
accounted for?
*To Show the Effect of Gravity on the Circulation.*--Hold one hand high
above the head, at the same time letting the other hand hang loosely by
the side. Observe the difference in the color of the hands and the degree
to which the large veins are filled. Repeat the experiment, reversing the
position of the hands. What results are observed? In what parts of the
body does gravity aid in the return of the blood to the heart? In what
parts does it hinder? Where fainting is caused by lack of blood in the
brain (the usual cause), is it better to let the patient lie down flat or
to force him into a sitting posture?
*To study the Circulation in a Frog's Foot* (Optional).--A compound
microscope is needed in this study and for extended examination it is best
to destroy the frog's brain. This is done by inserting some blunt-pointed
instrument into the skull cavity from the neck and moving it about. A
small frog, on account of the thinness of its webs, gives the best
results. It should be attached to a thin board which has an opening in one
end over which the web of the foot may be stretched. Threads should extend
from two of the toes to pins driven into the board to secure the necessary
tension of the web, and the foot and lower leg should be kept moist. Using
a two-thirds-inch objective, observe the branching of the small arteries
into the capillaries and the union of the capillaries to form the small
veins. The appearance is truly wonderful, but allowance must be made for
the fact that the _motion_ of the blood is magnified, as well as the
different structures, and that it appears to move much faster than it
really does. With a still higher power, the movements of the corpuscles
through the capillaries may be studied.
NOTE.--To perform this experiment without destroying the brain, the frog is
first carefully wrapped with strips of wet cloth and securely tied to the
board. The wrapping, while preventing movements of the frog, must not
interfere with the circulation.
CHAPTER VI - THE LYMPH AND ITS MOVEMENT THROUGH THE BODY
[Fig. 27]
Fig. 27--*Diagram showing position of the lymph* with reference to the
blood and the cells. The central tube is a capillary. The arrows indicate
the direction of slight movements in the lymph.
The blood, it will be remembered, moves everywhere through the body in a
system of _closed_ tubes. These keep it from coming in contact with any of
the cells of the body except those lining the tubes themselves. The
capillaries, to be sure, bring the blood very near the cells of the
different tissues; still, there is need of a liquid to fill the space
between the capillaries and the cells and to transfer materials from one
to the other. The lymph occupies this position and does this work. The
position of the lymph with reference to the capillaries and the cells is
shown in Fig. 27.
*Origin of the Lymph.*--The chief source of the lymph is the plasma of the
blood. As before described, the walls of the capillaries consist of a
single layer of flat cells placed edge to edge. Partly on account of the
pressure upon the blood and partly on account of the natural tendency of
liquids to pass through animal membranes, a considerable portion of the
plasma penetrates the thin walls and enters the spaces occupied by the
lymph.
The cells themselves also help to form the lymph, since the water and
wastes leaving the cells add to its bulk. These mix with the plasma from
the blood, forming the resultant liquid which is the lymph. A considerable
amount of the material absorbed from the food canal also enters the lymph
tubes, but this passes into the blood before reaching the cells.
*Composition and Physical Properties of the Lymph.*(26)--As would naturally
be expected, the composition of the lymph is similar to that of the blood.
In fact, nearly all the important constituents of the blood are found in
the lymph, but in different proportions. Food materials for the cells are
present in smaller amounts than in the blood, while impurities from the
cells are in larger amounts. As a rule the red corpuscles are absent from
the lymph, but the white corpuscles are present and in about the same
numbers as in the blood.
The physical properties of the lymph are also similar to those of the
blood. Like the blood, the lymph is denser than water and also coagulates,
but it coagulates more slowly than does the blood. The most noticeable
difference between these liquids is that of color, the lymph being
colorless. This is due to the absence of red corpuscles. The quantity of
lymph is estimated to be considerably greater than that of the blood.
*Lymph Vessels.*--Most of the lymph lies in minute cavities surrounding the
cells and in close relations with the capillaries (Figs. 27 and 30). These
are called _lymph spaces_. Connecting with the lymph spaces on the one
hand, and with certain blood vessels on the other, is a system of tubes
that return the lymph to the blood stream. The smallest of these, and the
ones in greatest abundance, are called _lymphatics_. They consist of
slender, thin-walled tubes, which resemble veins in structure, and, like
the veins, have valves. They differ from veins, however, in being more
uniform in size and in having thinner walls.
[Fig. 28]
Fig. 28--*Diagram of drainage system for the lymph.* 1. Thoracic duct. 2.
Right lymphatic duct. 3. Left subclavian vein. 4. Right subclavian vein.
5. Superior vena cava. 6. Lacteals. 7. Lymphatic glands. The small tubes
connecting with the lymph spaces in all parts of the body are the
lymphatics.
The lymphatics in different places gradually converge toward, and empty
into, the two main lymph tubes of the body. The smaller of these tubes,
called the _right lymphatic duct_, receives the lymph from the lymphatics
in the right arm, the right side of the head, and the region of the right
shoulder. It connects with, and empties its contents into, the right
subclavian vein at the place where it is joined by the right jugular vein
(Fig. 28).
The larger of the lymph tubes is called the _thoracic duct_. This receives
lymph from all parts of the body not drained by the right lymphatic duct,
and empties it into the left subclavian vein. Connection is made with the
subclavian vein on the upper side at the place where it is joined by the
left jugular vein. The thoracic duct has a length of from sixteen to
eighteen inches, and is about as large around as a goose quill. The lower
end terminates in an enlargement in the abdominal cavity, called the
_receptacle of the chyle_. It is provided with valves throughout its
course, in addition to one of considerable size which guards the opening
into the blood vessel.
The lymphatics which join the thoracic duct from the small intestine are
called the _lacteals_ (Fig. 28). These do not differ in structure from the
lymphatics in other parts of the body, but they perform a special work in
absorbing the digested fat (Chapter XI).
*Lymphatic Glands.*--The lymphatic glands, sometimes called lymph nodes,
are small and somewhat rounded bodies situated along the course of the
lymphatic tubes. They vary in size, some of them being an inch or more in
length. The lymph vessels generally open into them on one side and leave
them on the other (Figs. 28 and 30). They are not glands in function, but
are so called because of their having the general form of glands. They
provide favorable conditions for the development of white corpuscles (page
29). They also separate harmful germs and poisonous wastes from the lymph,
thereby preventing their entrance into the blood.
*Relations of the Lymph, the Blood, and the Cells.*--While the blood is
necessary as a carrying, or transporting, agent in the body, the lymph is
necessary for transferring materials from the blood to the cells and _vice
versa_. Serving as a physiological "go between," or medium of exchange,
the lymph enables the blood to minister to the needs of the cells. But the
lymph and the blood, everything considered, can hardly be looked upon as
two separate and distinct liquids. Not only do they supplement each other
in their work and possess striking similarities, but each is made in its
movements to pass into the vessels occupied by the other, so that they are
constantly mixing and mingling. For these and other reasons, they are more
properly regarded as two divisions of a single liquid--one which, by
adapting itself to different purposes,(27) supplies all the conditions of
a nutrient fluid for the cells.
*Movements of the Lymph.*--As compared with the blood, the lymph must be
classed as a quiet liquid. But, as already suggested, it has certain
movements which are necessary to the purposes which it serves. A careful
study shows it to have three well-defined movements as follows:
1. A movement from the capillaries toward the cells.
2. A movement from the cells toward the capillaries.
3. A movement of the entire body of lymph from the lymph spaces into the
lymphatics and along these channels to the ducts through which it enters
the blood.
By the first movement the cells receive their nourishment. By the second
and third movements the lymph, more or less laden with impurities, is
returned to the blood stream. (See Figs. 28 and 30.)
*Causes of the Lymph Movements.*--Let us consider first the movement
through the lymph tubes. No pump, like the heart, is known to be connected
with these tubes and to supply the pressure necessary for moving the
lymph. There are, however, several forces that indirectly aid in its flow.
The most important of these are as follows:
1. _Blood Pressure at the Capillaries._--The plasma which is forced through
the capillary walls by pressure from the heart makes room for itself by
pushing a portion of the lymph out of the lymph spaces. This in turn
presses upon the lymph in the tubes which it enters. In this way pressure
from the heart is transmitted to the lymph, forcing it to move.
2. _Variable Pressure on the Walls of the Lymph Vessels._--Pressure exerted
on the sides of the lymph tubes by contracting muscles tends to close them
up and to push the lymph past the valves, which, by closing, prevent its
return (Fig. 29). Pressure at the surface of the body, provided that it is
variable, also forces the lymph along. The valves in the lymph vessels
serve the same purpose as those in the veins.
[Fig. 29]
Fig. 29--*Diagram* to show how the muscles pump lymph. _A._ Relaxed muscle
beside which is a lymphatic tube. _B._ Same muscle in state of
contraction.
3. _The Inspiratory Force._--When the thoracic cavity is enlarged in
breathing, the unbalanced atmospheric pressure is exerted from all
directions towards the thoracic space. This not only causes the air to
flow into the lungs (Chapter VII), but also causes a movement of the blood
and lymph in such of their tubes as enter this cavity. It will be noted
that both of the large lymph ducts terminate where their contents may be
influenced by the respiratory movements. (See Practical Work.)
*Where the Lymph enters the Blood.*--The fact that the lymph is poured into
the blood at but two places, and these very close to each other, requires
a word of explanation. As a matter of fact, it is impossible for the lymph
to flow into blood vessels at most places on account of the blood
pressure. This would force the blood into the lymph vessels, instead of
allowing the lymph to enter the blood. The lymph can enter only at some
place where the blood pressure is less than the pressure that moves the
lymph. Such a place is found in the thoracic cavity. As already pointed
out (page 54), the blood pressure in the veins entering this cavity
becomes, with each expansion of the chest, negative, i.e., less than the
pressure of the atmosphere on the outside of the body. This, as we have
seen, aids in the flow of the blood into the right auricle. It also aids
in the passage of lymph into the blood vessels. The lymph is said to be
"sucked in," which means that it is forced in by the unbalanced pressure
of the atmosphere.(28) Some advantage is also gained by the lymph duct's
entering the subclavian vein on the upper side and at its union with the
jugular vein. Everything considered, it is found that the lymph flows into
the blood vessels where it can be "drawn in" by the movements of breathing
and where it meets with no opposition from the blood stream itself (Fig.
30).
[Fig. 30]
Fig. 30--*Diagram* showing general movement of lymph from the place of
relatively high pressure at the lymph spaces to the place of relatively
low pressure in the thoracic cavity.
*Lymph Movements at the Cells.*--The double movement of the lymph from the
capillaries toward the cells and from the cells toward the capillaries is
not entirely understood. Blood pressure in the capillaries undoubtedly has
much to do in forcing the plasma through the capillary walls, but this
tends to prevent the movement of the lymph in the opposite direction.
Movements between the blood and the lymph are known to take place in part
according to a general principle, known as _osmosis_, or dialysis.
[Fig. 31]
Fig. 31--*Vessel* with an upright membranous partition for illustrating
osmosis.
*Osmosis.*--The term "osmosis" is used to designate the passage of liquids
through some partition which separates them. Thus, if a vessel with an
upright membranous partition be filled on the one side with pure water and
on the other with water containing salt, an exchange of materials will
take place through the membrane until the same proportion of salt exists
on the two sides (Fig. 31). The cause of osmosis is the motion of the
molecules, or minute particles, that make up the liquid substance. If the
partition were not present, this motion would simply cause a mixing of the
liquids.
*Conditions under which Osmosis occurs.*--Osmosis may be shown by suitable
experiments (see Practical Work) to take place under the following
conditions:
1. The liquids on the two sides of the partition must be _unlike_ either
in density or in composition. Since the effect of the movement is to
reduce the liquids to the same condition, _a difference in density causes
the flow to be greater from the less dense toward the denser liquid_, than
in the opposite direction; while _a difference in composition causes the
substances in solution to move from the place of greater abundance toward
places of less abundance_.
2. The liquids must be capable of wetting, or penetrating, the partition.
If but one of the liquids penetrates the partition, the flow will be in
but one direction.
3. The liquids on the two sides of the partition must readily mix with
each other.
*Osmosis at the Cells.*--In the body osmosis takes place between the blood
and the lymph and between the lymph and the cells, the movements being
through the capillary walls and the membranes inclosing the cells (Fig.
27). Oxygen and food materials, which are found in great abundance in the
blood, are less abundant in the lymph and still less abundant in the
cells. According to the principle of osmosis, the main flow of oxygen and
food is from the capillaries toward the cells. On the other hand, the
wastes are most abundant in the cells where they are formed, less abundant
in the lymph, and least abundant in the blood. Hence the wastes flow from
the cells toward the capillaries.
*Solutions.*--Neither the blood plasma nor the lymph, as already shown, are
simple liquids; but they consist of water and different substances
dissolved in the water. They belong to a class of substances called
_solutions_. The chief point of interest about substances in solution is
that they are very finely divided and that their little particles are free
to move about in the liquid that contains them. Both the motion and the
finely divided condition of the dissolved substances are necessary to the
process of osmosis. All substances, however, that appear to be in solution
are not able to penetrate membranes, or take part in osmosis.
*Kinds of Solutions in the Body.*--The substances in solution in the body
liquids are of two general kinds known as _colloids_ and _crystalloids_.
The crystalloids are able to pass through membranous partitions, while the
colloids are not. An example of a colloid is found in the albumin of an
egg, which is unable to penetrate the membrane which surrounds it.
Examples of crystalloids are found in solutions of salt and sugar in
water. The inability of a colloid to penetrate a membrane is due to the
fact that it does not form a true solution. Its particles (molecules),
instead of being completely separated, still cling together, forming
little masses that are too large to penetrate the membrane. Since,
however, it has the appearance, on being mixed with water, of being
dissolved, it is called a _colloidal solution_. The crystalloid substance,
on the other hand, completely separates in the water and forms a _true
solution_--one which is able to penetrate the partition or membrane.
*Osmosis not a Sufficient Cause.*--The passage of materials through animal
membranes, according to the principle of osmosis, is limited to
crystalloid substances. But colloid substances are also known to pass
through the various partitions of the body. An example of such is found in
the proteids of the blood which, as a colloidal solution, pass through the
capillary walls to become a part of the lymph. Perhaps the best
explanation offered as yet for this passage is that the colloidal
substances are changed by the cells lining the capillaries into substances
that form true solutions and that after the passage they are changed back
again to the colloidal condition.
*Summary.*--Between the cells and the capillaries is a liquid, known as the
lymph, which is similar in composition and physical properties to the
blood. It consists chiefly of escaped plasma. The vessels that contain it
are connected with the system for the circulation of the blood. By adding
new material to the lymph and withdrawing waste material from it, the
blood keeps this liquid in a suitable condition for supplying the needs of
the cells. Supplementing each other in all respects, the blood and the
lymph together form the nutrient cell fluid of the body. The interchange
of material between the blood and the lymph, and the lymph and the cells,
takes place in part according to the principle of osmosis.
*Exercises.*--1. Explain the necessity for the lymph in the body.
2. Compare lymph and water with reference to density, color, and
complexity of composition.
3. Compare lymph and blood with reference to color, composition, and
movement through the body.
4. Show how blood pressure in the capillaries causes a flow of the lymph.
5. Show how contracting muscles cause the lymph to move. Compare with the
effect of muscular contraction upon the blood in the veins.
6. Trace the lymph in its flow from the right hand to where it enters the
blood; from the feet to where it enters the blood.
7. What conditions prevail at the cells to cause a movement of food and
oxygen in one direction and of waste materials in the opposite direction?
8. What part does water play in the exchanges at the cells?
9. Show that the blood and the lymph together fulfill all the requirements
of a nutrient cell fluid in the body.
PRACTICAL WORK
*To illustrate the Effect of Breathing upon the Flow of Lymph.*--Tightly
holding one end of a glass tube between the lips, let the other end extend
into water in a tumbler on a table. In this position quickly inhale air
through the nostrils, noting that with each inhalation there is a slight
movement of the water up the tube. (No sucking action should be exerted by
the mouth.) Apply to the movements in the large blood and lymph vessels
entering the thoracic cavity.
*To illustrate Osmosis.*--1. Separate the shell from the lining membrane at
one end of an egg, over an area about one inch in diameter. To do this
without injuring the membrane, the shell must first be broken into small
pieces and then picked off with a pair of forceps, or a small knife blade.
Fit a small glass tube, eight or ten inches long, into the other end so
that it will penetrate the membrane and pass down into the yolk. Securely
fasten the tube to the shell by melting beeswax around it, and set the egg
in a small tumbler partly filled with water. Examine in the course of half
an hour. What evidence now exists that the water has passed through the
membrane?
2. Tie over the large end of a "thistle tube" (used by chemists) a thin
animal membrane, such as a piece of the pericardium or a strip of the
membrane from around a sausage. Then fill the bulb and the lower end of
the tube with a concentrated solution of some solid, such as sugar, salt,
or copper sulphate. Suspend in a vessel of water so that the liquid which
it contains is just on a level with the water in the vessel. Examine from
time to time, looking for evidence of a movement in each direction through
the membrane. Why should the movement of the water into the tube be
greater than the movement in the opposite direction? (If the thistle tube
has a very slender stem, it is better to fill the bulb before tying on the
membrane. The opening in the stem may be plugged during the process of
filling.)
[Fig. 32]
Fig. 32--An osmosometer.
NOTE.--With a special piece of apparatus, known as an _osmosometer_, the
principle of osmosis may be more easily illustrated than by the method in
either of the above experiments (Fig. 32). This apparatus may be obtained
from supply houses.
CHAPTER VII - RESPIRATION
Through the movements of the blood and the lymph, materials entering the
body are transported to the cells, and wastes formed at the cells are
carried to the organs which remove them from the body. We are now to
consider the passage of materials from outside the body to the cells and
_vice versa_. One substance which the body constantly needs is oxygen, and
one which it is constantly throwing off is carbon dioxide. Both of these
are constituents of
*The Atmosphere.*--The atmosphere, or air, completely surrounds the earth
as a kind of envelope, and comes in contact with everything upon its
surface. It is composed chiefly of oxygen and nitrogen,(29) but it also
contains a small per cent of other substances, such as water-vapor, carbon
dioxide, and argon. All of the regular constituents of the atmosphere are
gases, and these, as compared with liquids and solids, are very light.
Nevertheless the atmosphere has weight and, on this account, exerts
pressure upon everything on the earth. At the sea level, its pressure is
nearly fifteen pounds to the square inch. The atmosphere forms an
essential part of one's physical environment and serves various purposes.
The process by which gaseous materials are made to pass between the body
and the atmosphere is known as
*Respiration.*--As usually defined, respiration, or breathing, consists of
two simple processes--that of taking air into special contrivances in the
body, called the lungs, and that of expelling air from the lungs. The
first process is known as _inspiration_; the second as _expiration_. We
must, however, distinguish between respiration by the lungs, called
_external respiration_, and respiration by the cells, called _internal
respiration_.
_The purpose of respiration_ is indicated by the changes that take place
in the air while it is in the lungs. Air entering the lungs in ordinary
breathing parts with about five per cent of itself in the form of oxygen
and receives about four and one half per cent of carbon dioxide,
considerable water-vapor, and a small amount of other impurities. These
changes suggest a twofold purpose for respiration:
1. To obtain from the atmosphere the supply of oxygen needed by the body.
2. To transfer to the atmosphere certain materials (wastes) which must be
removed from the body.
The chief organs concerned in the work of respiration are
*The Lungs.*--The lungs consist of two sac-like bodies suspended in the
thoracic cavity, and occupying all the space not taken up by the heart.
They are not simple sacs, however, but are separated into numerous
divisions, as follows:
1. The lung on the right side of the thorax, called the right lung, is
made up of three divisions, or _lobes_, and the left lung is made up of
two lobes.
2. The lobes on either side are separated into smaller divisions, called
_lobules_ (Fig. 33). Each lobule receives a distinct division of an air
tube and has in itself the structure of a miniature lung.
[Fig. 33]
Fig. 33--*Lungs and air passages* seen from the front. The right lung shows
the lobes and their divisions, the lobules. The tissue of the left lung
has been dissected away to show the air tubes.
3. In the lobule the air tube divides into a number of smaller tubes, each
ending in a thin-walled sac, called an _infundibulum_. The interior of the
infundibulum is separated into many small spaces, known as the _alveoli_,
or air cells.
The lungs are remarkable for their lightness and delicacy of
structure.(30) They consist chiefly of the tissues that form their sacs,
air tubes, and blood vessels; the membranes that line their inner and
outer surfaces; and the connective tissue that binds these parts together.
All these tissues are more or less elastic. The relation of the different
parts of the lungs to each other and to the outside atmosphere will be
seen through a study of the
*Air Passages.*--The air passages consist of a system of tubes which form a
continuous passageway between the outside atmosphere and the different
divisions of the lungs. The air passes through them as it enters and
leaves the lungs, a fact which accounts for the name.
[Fig. 34]
Fig. 34--*Model of section through the head*, showing upper air passages
and other parts. 1. Left nostril. 2. Pharynx. 3. Tongue and cavity of
mouth. 4. Larynx. 5. Trachea. 6. Esophagus.
The incoming air first enters the _nostrils_. These consist of two narrow
passages lying side by side in the nose, and connecting with the pharynx
behind. The lining of the nostrils, called _mucous membrane_ is quite
thick, and has its surface much extended by reason of being spread over
some thin, scroll-shaped bones that project into the passage. This
membrane is well supplied with blood vessels and secretes a considerable
quantity of liquid. Because of the nature and arrangement of the membrane,
the nostrils are able to _warm_ and _moisten_ the incoming air, and to
_free it from dust particles_, preparing it, in this way, for entrance
into the lungs (Fig. 34).
The nostrils are separated from the mouth by a thin layer of bone, and
back of both the mouth and the nostrils is the pharynx. The _pharynx_ and
the _mouth_ serve as parts of the food canal, as well as air passages, and
are described in connection with the organs of digestion (Chapter X). Air
entering the pharynx, either by the nostrils or by the mouth, passes
through it into the _larynx_. The larynx, being the special organ for the
production of the voice, is described later (Chapter XXI). The entrance
into the larynx is guarded by a movable lid of cartilage, called the
_epiglottis_, which prevents food particles and liquids, on being
swallowed, from passing into the lower air tubes. The relations of the
nostrils, mouth, pharynx, and larynx are shown in Fig. 34.
From the larynx the air enters the _trachea_, or windpipe. This is a
straight and nearly round tube, slightly less than an inch in diameter and
about four and one half inches in length. Its walls contain from sixteen
to twenty C-shaped, cartilaginous rings, one above the other and
encircling the tube. These incomplete rings, with their openings directed
backward, are held in place by thin layers of connective and muscular
tissue. At the lower end the trachea divides into two branches, called the
bronchi, each of which closely resembles it in structure. Each _bronchus_
separates into a number of smaller divisions, called the _bronchial
tubes_, and these in turn divide into still smaller branches, known as the
_lesser bronchial tubes_ (Fig. 33). The lesser bronchial tubes, and the
branches into which they separate, are the smallest of the air tubes. One
of these joins, or expands into, each of the minute lung sacs, or
infundibula. Mucous membrane lines all of the air passages.
*General Condition of the Air Passages.*--One necessary condition for the
movement of the air into and from the lungs is an unobstructed
passageway.(31) The air passages must be kept open and free from
obstructions. They are _kept open_ by special contrivances found in their
walls, which, by supplying a degree of stiffness, cause the tubes to keep
their form. In the trachea, bronchi, and larger bronchial tubes, the
stiffness is supplied by rings of cartilage, while in the smaller tubes
this is replaced by connective and muscular tissue. The walls of the
larynx contain strips and plates of cartilage; while the nostrils and the
pharynx are kept open by their bony surroundings.
[Fig. 35]
Fig. 35--*Ciliated epithelial cells.* _A._ Two cells highly magnified. _c._
Cilia, _n._ Nucleus. _B._ Diagram of a small air tube showing the lining
of cilia.
The air passages are _kept clean_ by cells especially adapted to this
purpose, known as the _ciliated epithelial cells_. These are slender,
wedge-shaped cells which have projecting from a free end many small,
hair-like bodies, called _cilia_ (Fig. 35). They line the mucous membrane
in most of the air passages, and are so placed that the cilia project into
the tubes. Here they keep up an inward and outward wave-like movement,
which is quicker and has greater force in the _outward_ direction. By this
means the cilia are able to move small pieces of foreign matter, such as
dust particles and bits of partly dried mucus, called phlegm, to places
where they can be easily expelled from the lungs.(32)
[Fig. 36]
Fig. 36--*Terminal air sacs.* The two large sacs are infundibula; the small
divisions are alveoli. (Enlarged.)
*The Alveoli.*--The alveoli, or air cells, are the small divisions of the
infundibula (Fig. 36). They are each about one one-hundredth of an inch
(1/4 mm.) in diameter, being formed by the infolding of the infundibular
wall. This wall, which has for its framework a thin layer of elastic
connective tissue, supports a dense network of capillaries (Fig. 37), and
is lined by a single layer of cells placed edge to edge. By this
arrangement the air within the alveoli is brought very near a large
surface of blood, and the exchange of gases between the air and the blood
is made possible. It is at the alveoli that the oxygen passes from the air
into the blood, and the carbon dioxide passes from the blood into the air.
At no place in the lungs, however, do the air and the blood come in direct
contact. Their exchanges must in all cases take place through the
capillary walls and the layer of cells lining the alveoli.
[Fig. 37]
Fig. 37--*Inner lung surface (magnified)*, the blood vessels injected with
coloring matter. The small pits are alveoli, and the vessels in their
walls are chiefly capillaries.
[Fig. 38]
Fig. 38.--*Diagram to show the double movement of air and blood through the
lungs.* The blood leaves the heart by the pulmonary artery and returns by
the pulmonary veins. The air enters and leaves the lungs by the same
system of tubes.
[Fig. 39]
Fig. 39--*Diagram to show air and blood movements in a terminal air sac.*
While the air moves into and from the space within the sac, the blood
circulates through the sac walls.
*Blood Supply to the Lungs.*--To accomplish the purposes of respiration,
not only the air, but the blood also, must be passed into and from the
lungs. The chief artery conveying blood to the lungs is the _pulmonary
artery_. This starts at the right ventricle and by its branches conveys
blood to the capillaries surrounding the alveoli in all parts of the
lungs. The branches of the pulmonary artery lie alongside of, and divide
similarly to, the bronchial tubes. At the places where the finest
divisions of the air tubes enter the infundibula, the little arteries
branch into the capillaries that penetrate the infundibular walls (Figs.
38 and 39). From these capillaries the blood is conveyed by the pulmonary
veins to the left auricle.
The lungs also receive blood from two (in some individuals three) small
arteries branching from the aorta, known as the _bronchial arteries_.
These convey to the lungs blood that has already been supplied with
oxygen, passing it into the capillaries in the walls of the bronchi,
bronchial tubes, and large blood vessels, as well as the connective tissue
between the lobes of the lungs. This blood leaves the lungs partly by the
bronchial veins and partly by the pulmonary veins. No part of the body is
so well supplied with blood as the lungs.
[Fig. 40]
Fig. 40--*The pleurae.* Diagram showing the general form of the pleural sacs
as they surround the lungs and line the inner surfaces of the chest (other
parts removed). _A, A'._ Places occupied by the lungs. _B, B'._ Slight
space within the pleural sacs containing the pleural secretion, _a, a'._
Outer layer of pleura and lining of chest walls and upper surface of
diaphragm. _b, b'._ Inner layer of pleura and outer lining of lungs. _C._
Space occupied by the heart. _D._ Diaphragm.
*The Pleura.*--The pleura is a thin, smooth, elastic, and tough membrane
which covers the outside of the lungs and lines the inside of the chest
walls. The covering of each lung is continuous with the lining of the
chest wall on its respective side and forms with it a closed sac by which
the lung is surrounded, the arrangement being similar to that of the
pericardium. Properly speaking, there are two pleurae, one for each lung,
and these, besides inclosing the lungs, partition off a middle space which
is occupied by the heart (Fig. 40). They also cover the upper surface of
the diaphragm, from which they deflect upward, blending with the
pericardium. A small amount of liquid is secreted by the pleura, which
prevents friction as the surfaces glide over each other in breathing.
*The Thorax.*--The force required for breathing is supplied by the box-like
portion of the body in which the lungs are placed. This is known as the
thorax, or chest, and includes that part of the trunk between the neck and
the abdomen. The space which it incloses, known as the thoracic cavity, is
a _variable_ space and the walls surrounding this space are _air-tight._ A
framework for the thorax is supplied by the ribs which connect with the
spinal column behind and with the sternum, or breast-bone, in front. They
form joints with the spinal column, but connect with the sternum by strips
of cartilage. The ribs do not encircle the cavity in a horizontal
direction, but slope downward from the spinal column both toward the front
and toward the sides, this being necessary to the service which they
render in breathing.
*How Air is Brought into and Expelled from the Lungs.*--The principle
involved in breathing is that air flows from a place of _greater_ to a
place of _less_ pressure. The construction of the thorax and the
arrangement of the lungs within it provide for the application of this
principle in a most practical manner. The lungs are suspended from the
upper portion of the thoracic cavity, and the trachea and the upper air
passages provide the only opening to the outside atmosphere. Air entering
the thorax must on this account pass into the lungs. As the thorax is
enlarged the air in the lungs expands, and there is produced within them a
place of _slightly less_ air pressure than that of the atmosphere on the
outside of the body. This difference causes the air to flow into the
lungs.
[Fig. 41]
Fig. 41--*Diagram illustrating the bellows principle in breathing.* _A._
The human bellows. _B._ The hand bellows. Compare part for part.
When the thorax is diminished in size, the air within the lungs is
slightly compressed. This causes it to become denser and to exert on this
account a pressure _slightly greater_ than that of the atmosphere on the
outside. The air now flows out until the equality of the pressure is again
restored. Thus the thorax, by making the pressure within the lungs first
slightly less and then slightly greater than the atmospheric pressure,
causes the air to move into and out of the lungs.
Breathing is well illustrated by means of the common hand bellows, its
action being similar to that of the thorax. It will be observed that when
the sides are spread apart air flows into the bellows. When they are
pressed together the air flows out. If an air-tight sack were hung in the
bellows with its mouth attached to the projecting tube, the arrangement
would resemble closely the general plan of the breathing organs (Fig. 41).
One respect, however, in which the bellows differs from the thorax should
be noted. The thorax is never sufficiently compressed to drive out all the
air. Air is always present in the lungs. This keeps them more or less
distended and pressed against the thoracic walls.
*How the Thoracic Space is Varied.*--One means of varying the size of the
thoracic cavity is through the movements of the ribs and their resultant
effect upon the walls of the thorax. In bringing about these movements the
following muscles are employed:
1. The _scaleni_ muscles, three in number on each side, which connect at
one end with the vertebrae of the neck and at the other with the first and
second ribs. Their contraction slightly raises the upper portion of the
thorax.
2. The _elevators of the ribs_, twelve in number on each side, which are
so distributed that each single muscle is attached, at one end, to the
back portion of a rib and, at the other, to a projection of the vertebra a
few inches above. The effect of their contraction is to' elevate the
middle portion of the ribs and to turn them outward or spread them apart.
3. The _intercostal_ muscles, which form two thin layers between the ribs,
known as the _internal_ and the _external_ intercostal muscles. The
external intercostals are attached between the outer lower margin of the
rib above and the outer upper margin of the rib below, and extend
obliquely downward and forward. The internal intercostals are attached
between the inner margins of adjacent ribs, and they extend obliquely
downward and backward from the front. The contraction of the external
intercostal muscles raises the ribs, and the contraction of the internal
intercostals tends to lower them.
[Fig. 42]
Fig. 42--*Simple apparatus* for illustrating effect of movements of the
ribs upon the thoracic space; strips of cardboard held together by pins,
the front part being raised or lowered by threads moving through
attachments at 1 and 2. As the front is raised the space between the
uprights is increased. The front upright corresponds to the breastbone,
the back one to the spinal column, the connecting strips to the ribs, and
the threads to the intercostal muscles.
By slightly raising and spreading apart the ribs the thoracic space is
increased in two directions--from front to back and from side to side.
Lowering and converging the ribs has, of course, the opposite effect (Fig.
42). Except in forced expirations the ribs are lowered and converged by
their own weight and by the elastic reaction of the surrounding parts.
*The Diaphragm.*--Another means of varying the thoracic space is found in
an organ known as the diaphragm. This is the dome-shaped, _movable
partition_ which separates the thoracic cavity from the cavity of the
abdomen. The edges of the diaphragm are firmly attached to the walls of
the trunk, and the center is supported by the pericardium and the pleura.
The outer margin is muscular, but the central portion consists of a strong
sheet of connective tissue. By the contraction of its muscles the
diaphragm is pulled down, thereby increasing the thoracic cavity. By
raising the diaphragm the thoracic cavity is diminished.
The diaphragm, however, is not raised by the contraction of its own
muscles, but _is pushed up_ by the organs beneath. By the elastic reaction
of the abdominal walls (after their having been pushed out by the lowering
of the diaphragm), pressure is exerted on the organs of the abdomen and
these in turn press against the diaphragm. This crowds it into the
thoracic space. In forced expirations the muscles in the abdominal walls
contract to push up the diaphragm.
*Interchange of Gases in the Lungs.*--During each inspiration the air from
the outside fills the entire system of bronchial tubes, but the alveoli
are largely filled, at the same time, by the air which the last expiratory
effort has left in the passages. By the action of currents and eddies and
by the rapid diffusion of gas particles, the air from the outside mixes
with that in the alveoli and comes in contact with the membranous walls.
Here the oxygen, after being dissolved by the moisture in the membrane,
diffuses into the blood. The carbon dioxide, on the other hand, being in
excess in the blood, diffuses toward the air in the alveoli. The
interchange of gases at the lungs, however, is not fully understood, and
it is possible that other forces than osmosis play a part.
[Fig. 43]
Fig. 43--*Diagram* illustrating lung capacity.
*Capacity of the Lungs.*--The air which passes into and from the lungs in
ordinary breathing, called the _tidal_ air, is but a small part of the
whole amount of air which the lungs contain. Even after a forced
expiration the lungs are almost half full; the air which remains is called
the _residual_ air. The air which is expelled from the lungs by a forced
expiration, less the tidal air, is called the _reserve_, or supplemental,
air. These several quantities are easily estimated. (See Practical Work.)
In the average individual the total capacity of the lungs (with the chest
in repose) is about one gallon. In forced inspirations this capacity may
be increased about one third, the excess being known as the _complemental_
air (Fig. 43).
[Fig. 44]
Fig. 44--*Diagram* illustrating internal respiration and its dependence on
external respiration. (Modified from Hall.) (See text.)
*Internal, or Cell, Respiration.*--The oxygen which enters the blood in the
lungs leaves it in the tissues, passing through the lymph into the cells
(Fig. 44). At the same time the carbon dioxide which is being formed at
the cells passes into the blood. An exchange of gases is thus taking place
between the cells and the blood, similar to that taking place between the
blood and the air. This exchange is known as _internal_, or cell,
respiration. By internal respiration the oxygen reaches the place where it
is to serve its purpose, and the carbon dioxide begins its movement toward
the exterior of the body. This "breathing by the cells" is, therefore,
_the final and essential act of respiration_. Breathing by the lungs is
simply the means by which the taking up of oxygen and *the* giving off of
carbon dioxide by the cells is made possible.
HYGIENE OF RESPIRATORY ORGANS
The liability of the lungs to attacks from such dread diseases as
consumption and pneumonia makes questions touching their hygiene of first
importance. Consumption does not as a rule attack sound lung tissue, but
usually has its beginning in some weak or enfeebled spot in the lungs
which has lost its "power of resistance." Though consumption is not
inherited, as some suppose, lung weaknesses may be transmitted from
parents to children. This, together with the fact, now generally
recognized, that consumption is contagious, accounts for the frequent
appearance of this disease in the same family. Consumption as well as
other respiratory affections can in the majority of cases be _prevented_,
and in many cases cured, by an intelligent observation of well-known laws
of health.
*Breathe through the Nostrils.*--Pure air and plenty of it is the main
condition in the hygiene of the lungs. One necessary provision for
obtaining _pure air_ is that of breathing through the nostrils. Air is the
carrier of dust particles and not infrequently of disease germs.(33)
Partly through the small hairs in the nose, but mainly through the moist
membrane that lines the passages, the nostrils serve as filters for
removing the minute solid particles (Fig. 45). While it is important that
nose breathing be observed at all times, it is especially important when
one is surrounded by a dusty or smoky atmosphere. Otherwise the small
particles that are breathed in through the mouth may find a lodging place
in the lungs.
[Fig. 45]
Fig. 45--*Human air filter.* Diagram of a section through the nostrils;
shows projecting bones covered with moist membrane against which the air
is made to strike by the narrow passages. 1. Air passages. 2. Cavities in
the bones. 3. Front lower portion of the cranial cavity.
In addition to removing dust particles and germs, other purposes are
served by breathing through the nostrils. The warmth and moisture which
the air receives in this way, prepare it for entering the lungs. Mouth
breathing, on the other hand, looks bad and during sleep causes snoring.
The habit of nose breathing should be established early in life.(34)
*Cultivate Full Breathing.*--Many people, while apparently taking in
sufficient air to supply their need for oxygen, do not breathe deeply
enough to "freely ventilate the lungs." "Shallow breathing," as this is
called, is objectionable because it fails to keep up a healthy condition
of the entire lung surface. Portions of the lungs to which air does not
easily penetrate fail to get the fresh air and exercise which they need.
As a consequence, they become weak and, by losing their "power of
resistance," become points of attack in diseases of the lungs.(35) The
breathing of each individual should receive attention, and where from some
cause it is not sufficiently full and deep, the means should be found for
remedying the defect.
*Causes of Shallow Breathing.*--Anything that impedes the free movement of
air into the lungs tends to cause shallow breathing A drooping of the back
or shoulders and a curved condition of the spinal column, such as is
caused by an improper position in sitting, interfere with the free
movements of the ribs and are recognized causes. Clothing also may impede
the respiratory movements and lead to shallow breathing. If too tight
around the chest, clothing interferes with the elevation of the ribs; and
if too tight around the waist, it prevents the depression of the
diaphragm. Other causes of shallow breathing are found in the absence of
vigorous exercise, in the leading of an indoor and inactive life, in
obstructions in the nostrils and upper pharynx, and in the lack of
attention to proper methods of breathing.
To prevent shallow breathing one should have the habit of sitting and
standing erect. The clothing must not be allowed to interfere with the
respiratory movements. The taking of exercise sufficiently vigorous to
cause deep and rapid breathing should be a common practice and one should
spend considerable time out of doors. If one has a flat chest or round
shoulders, he should strive by suitable exercises to overcome these
defects. Obstructions in the nostrils or pharynx should be removed.
*Breathing Exercises.*--In overcoming the habit of shallow breathing and in
strengthening the lungs generally, the practicing of occasional deep
breathing has been found most valuable and is widely recommended. With the
hands on the hips, the shoulders drawn back and _down_, the chest pushed
upward and forward, and the chin slightly depressed, draw the air slowly
through the nostrils until the lungs are _completely_ full. After holding
this long enough to count three slowly, expel it quickly from the lungs.
Avoid straining. To get the benefit of pure air, it is generally better to
practice deep breathing out of doors or before an open window.
By combining deep breathing with simple exercises of the arms, shoulders,
and trunk much may be done towards straightening the spine, squaring the
shoulders, and overcoming flatness of the chest. Though such movements are
best carried on by the aid of a physical director, one can do much to help
himself. One may safely proceed on the principle that slight deformities
of the chest, spine, and shoulders are corrected by gaining and keeping
the natural positions, and may employ any movements which will loosen up
the parts and bring them where they naturally belong.(36)
*Serious Nature of Colds.*--That many cases of consumption have their
beginning in severe colds (on the lungs) is not only a matter of popular
belief, but the judgment also of physicians. Though the cold is a
different affection from that of consumption, it may so lower the vitality
of the body and weaken the lung surfaces that the germs of consumption
find it easy to get a start. On this account a cold on the chest which
does not disappear in a few days, but which persists, causing more or less
coughing and pain in the lungs, must be given serious consideration.(37)
The usual home remedies failing to give relief, a physician should be
consulted. It should also be noted that certain diseases of a serious
nature (pneumonia, diphtheria, measles, etc.) have in their beginning the
appearance of colds. On this account it is wise not only to call a
physician, but to call him early, in severe attacks of the lungs.
Especially if the attack be attended by difficult breathing, fever, and a
rapid pulse is the case serious and medical advice necessary.
*Ventilation.*--The process by which the air in a room is kept fresh and
pure is known as ventilation. It is a double process--that of bringing
fresh air into the room and that of getting rid of air that has been
rendered impure by breathing (38) or by lamps. Outdoor air is usually of a
different temperature (colder in winter, warmer in summer) from that
indoors, and as a consequence differs from it slightly in weight. On
account of this difference, suitable openings in the walls of buildings
induce currents which pass between the rooms and the outside atmosphere
even when there is no wind. In winter care must be taken to prevent drafts
and to avoid too great a loss of heat from the room. A cold draft may even
cause more harm to one in delicate health than the breathing of air which
is impure. To ventilate a room successfully the problem of preventing
drafts must be considered along with that of admitting the fresh air.
[Fig. 46]
Fig. 46--Window adjusted for ventilation without drafts.
The method of ventilation must also be adapted to the construction of the
building, the plan of heating, and the condition of the weather. Specific
directions cannot be given, but the following suggestions will be found
helpful in ventilating rooms where the air is not warmed before being
admitted:
1. _Introduce, the air through many small openings_ rather than a few
large ones. If the windows are used for this purpose, raise the lower sash
and drop the upper one _slightly_ for _several_ windows, varying the width
to suit the conditions (Fig. 46). By this means sufficient air may be
introduced without causing drafts.
2. _Introduce the air at the warmest portions of the room._ The air
should, if possible, be warmed before reaching the occupants.
3. If the wind is blowing, _ventilate principally on the sheltered side of
the house_.
Ample provision should be made for fresh air in sleeping rooms, and here
again drafts must be avoided. Especially should the bed be so placed that
strong air currents do not pass over the sleeper. In schoolhouses and
halls for public gatherings the means for efficient ventilation should, if
possible, be provided in the general plan of construction and method of
heating.
[Fig. 47]
Fig. 47--*Artificial respiration* as a laboratory experiment. Expiration.
Prone-posture method of Schaffer.
*Artificial Respiration.*--When natural breathing is temporarily suspended,
as in partial drowning, or when one has been overcome by breathing some
poisonous gas, the saving of life often depends upon the prompt
application of artificial respiration. This is accomplished by alternately
compressing and enlarging the thorax by means of variable pressure on the
outside, imitating the natural process as nearly as possible. Following is
the method proposed by Professor E.A. Schaffer of England, and called by
him "the _prone-posture_ method of artificial respiration":
The patient is laid face downward with an arm bent under the head, and
_intermittent_ pressure applied vertically over the shortest ribs. The
pressure drives the air from the lungs, both by compressing the lower
portions of the chest and by forcing the abdominal contents against the
diaphragm, while the elastic reaction of the parts causes fresh air to
enter (Figs. 47 and 48). "The operator kneels or squats by the side of, or
across the patient, places his hands over the lowest ribs and swings his
body backward and forward so as to allow his weight to fall vertically on
the wrists and then to be removed; in this way hardly any muscular
exertion is required.... The pressure is applied gradually and slowly,
occupying some three seconds; it is then withdrawn during two seconds and
again applied; and so on some twelve times per minute."(39)
[Fig. 48]
Fig. 48--Artificial respiration. Inspiration.
The special advantages of the prone-posture method over others that have
been employed are: I. It may be applied by a single individual and fora
long period of time without exhaustion. 2. It allows the mucus and water
(in case of drowning) to run out of the mouth, and causes the tongue to
fall forward so as not to obstruct the passageway. 3. It brings a
sufficient amount of air into the lungs.(40)
While applying artificial respiration, the heat of the body should not be
allowed to escape any more than can possibly be helped. In case of
drowning, the patient should be wrapped in dry blankets or clothing, while
bottles of hot water may be placed in contact with the body. The
circulation should be stimulated, as may be done by rubbing the hands,
feet, or limbs in the direction of the flow of the blood in the veins.
*Tobacco Smoke and the Air* Passages.--Smoke consists of minute particles
of unburnt carbon, or soot, such as collect in the chimneys of fireplaces
and furnaces. If much smoke is taken into the lungs, it irritates the
delicate linings and tends to clog them up. Tobacco smoke also contains
the poison nicotine, which is absorbed into the blood. For these reasons
the cigarette user who inhales the smoke does himself great harm, injuring
his nervous system and laying the foundation for diseases of the air
passages. The practice of smoking indoors is likewise objectionable, since
every one in a room containing the smoke is compelled to breathe it.
*Alcohol and Diseases of the Lungs.*--Pneumonia is a serious disease of the
lungs caused by germs. The attacks occur as a result of exposure,
especially when the body is in a weakened condition. A noted authority
states that "alcoholism is perhaps the most potent predisposing cause" of
pneumonia.(41) A person addicted to the use of alcohol is also less likely
to recover from the disease than one who has avoided its use, a result due
in part to the weakening effect of alcohol upon the heart. The congestion
of the lungs in pneumonia makes it very difficult for the heart to force
the blood through them. The weakened heart of the drunkard gives way under
the task.
The statement sometimes made that alcohol is beneficial in pulmonary
tuberculosis is without foundation in fact. On the other hand, alcoholism
is a recognized cause of consumption. Some authorities claim that this
disease is more frequent in heavy drinkers than in those of temperate
habits, in the proportion of about three to one, and that possibly half of
the cases of tuberculosis are traceable to alcoholism.(42)
*The Outdoor Cure for Lung Diseases*--Among the many remedies proposed for
consumption and kindred diseases, none have proved more beneficial,
according to reports, than the so-called "outdoor" cure. The person having
consumption is fed plentifully upon the most nourishing food, and is made
to spend practically his entire time, including the sleeping hours, _out
of doors_. Not only is this done during the pleasant months of summer, but
also during the winter when the temperature is below freezing. Severe
exposure is prevented by overhead protection at night and by sufficient
clothing to keep the body warm. The abundant supply of pure, cold air
toughens the lungs and invigorates the entire body, thereby enabling it to
throw off the disease.
The success attending this method of treating consumptives suggests the
proper mode of strengthening lungs that are not diseased, but simply weak.
The person having weak lungs should spend as much time as he conveniently
can out of doors. He should provide the most ample ventilation at night
and have a sleeping room to himself. He should practice deep breathing
exercises and partake of a nourishing diet. While avoiding prolonged
chilling and other conditions liable to induce colds, he should take
advantage of every opportunity of exposing himself fully and freely to the
outside atmosphere.
*Summary.*--The purpose of respiration is to bring about an exchange of
gases between the body and the atmosphere. The organs employed for this
purpose, called the respiratory organs, are adapted to handling materials
in the _gaseous_ state, and are operated in accordance with principles
governing the movements of the atmosphere. By alternately increasing and
diminishing the thoracic space, air is made to pass between the outside
atmosphere and the interior of the lungs. Finding its way into the
smallest divisions of the lungs, called the alveoli, the air comes very
near a large surface of blood. By this means the carbon dioxide diffuses
out of the blood, and the free oxygen enters. Through the combined action
of the organs of respiration and the organs that move the blood and the
lymph, the cells in all parts of the body are enabled to exchange certain
gaseous materials with the outside atmosphere.
[Fig. 49]
Fig. 49--Model for demonstrating the lungs.
*Exercises.--*1. How does air entering the lungs differ in composition from
air leaving the lungs? What purposes of respiration are indicated by these
differences?
2. Name the divisions of the lungs.
3. Trace air from the outside atmosphere into the alveoli. Trace the blood
from the right ventricle to the alveoli and back again to the left
auricle.
4. How does the movement of air into and from the lungs differ from that
of the blood through the lungs with respect to (_a_) the direction of the
motion. (_b_) the causes of the motion, and (_c_) the tubes through which
the motion takes place?
5. How are the air passages kept clean and open?
6. Describe the pleura. Into what divisions does it separate the thoracic
cavity?
7. Describe and name uses of the diaphragm.
8. If 30 cubic inches of air are passed into the lungs at each inspiration
and .05 of this is retained as oxygen, calculate the number of cubic feet
of oxygen consumed each day, if the number of inspirations be 18 per
minute.
9. Find the _weight_ of a day's supply of oxygen, as found in the above
problem, allowing 1.3 ounces as the weight of a cubic foot.
10. Make a study of the hygienic ventilation of the schoolroom.
11. Give advantages of full breathing over shallow breathing.
12. How may a flat chest and round shoulders be a cause of consumption?
How may these deformities be corrected?
13. Give general directions for applying artificial respiration.
PRACTICAL WORK
Examine a dissectible model of the chest and its contents (Fig. 49). Note
the relative size of the two lungs and their position with reference to
the heart and diaphragm. Compare the side to side and vertical diameters
of the cavity. Trace the air tubes from the trachea to their smallest
divisions.
*Observation of Lungs* (Optional).--Secure from a butcher the lungs of a
sheep, calf, or hog. The windpipe and heart should be left attached and
the specimen kept in a moist condition until used. Demonstrate the
trachea, bronchi, and the bronchial tubes, and the general arrangement of
pulmonary arteries and veins. Examine the pleura and show lightness of
lung tissue by floating a piece on water.
*To show the Changes that Air undergoes in the Lungs.*--1. Fill a quart jar
even full of water. Place a piece of cardboard over its mouth and invert,
without spilling, in a pan of water. Inserting a tube under the jar, blow
into it air that has been held as long as possible in the lungs. When
filled with air, remove the jar from the pan, keeping the top well
covered. Slipping the cover slightly to one side, insert a burning
splinter and observe that the flame is extinguished. This proves the
absence of sufficient oxygen to support combustion. Pour in a little
limewater(43) and shake to mix with the air. The change of the limewater
to a milky white color proves the presence of carbon dioxide.
[Fig. 50]
Fig. 50--*Apparatus* for showing changes which air undergoes while in the
lungs.
2. The effects illustrated in experiment 1 may be shown in a somewhat more
striking manner as follows: Fill two bottles of the same size each one
fourth full of limewater and fit each with a two-holed rubber stopper
(Fig. 50). Fit into each stopper one short and one long glass tube, the
long tube extending below the limewater. Connect the short tube of one
bottle and the long tube of the other bottle with a Y-tube. Now breathe
slowly three or four times through the Y-tube. It will be found that the
inspired air passes through one bottle and the expired air through the
other. Compare the effect upon the limewater in the two bottles. Insert a
small burning splinter into the top of each bottle and note result. What
differences between inspired and expired air are thus shown?
3. Blow the breath against a cold window pane. Note and account for the
collection of moisture.
4. Note the temperature of the room as shown by a thermometer. Now breathe
several times upon the bulb, noting the rise in the mercury. What does
this experiment show the body to be losing through the breath?
*To show Changes in the Thoracic Cavity.*--1. To a yard- or meter-stick,
attach two vertical strips, each about eight inches long, as shown in Fig.
51. The piece at the end should be secured firmly in place by screws or
nails. The other should be movable. With this contrivance measure the
sideward and forward expansion of a boy's thorax. Take the diameter first
during a complete inspiration and then during a complete expiration,
reading the difference. Compare the forward with the sideward expansion.
[Fig. 51]
Fig. 51--*Apparatus* for measuring chest expansion.
2. With a tape-line take the circumference of the chest when all the air
possible has been expelled from the lungs. Take it again when the lungs
have been fully inflated. The difference is now read as the chest
expansion.
[Fig. 52]
Fig. 52--*Simple apparatus* for illustrating the action of the diaphragm.
*To illustrate the Action of the Diaphragm.*--Remove the bottom from a
large bottle having a small neck. (Scratch a deep mark with a file and
hold on the end of this mark a hot poker. When the glass cracks, lead the
crack around the bottle by heating about one half inch in advance of it.)
Place the bottle in a large glass jar filled two thirds full of water
(Fig. 52). Let the space above the water represent the chest cavity and
the water surface represent the diaphragm. Raise the bottle, noting that
the water falls, thereby increasing the space and causing air to enter.
Then lower the bottle, noting the opposite effect. To show the movement of
the air in and out of the bottle, hold with the hand (or arrange a support
for) a burning splinter over the mouth of the bottle.
*To estimate the Capacity of the Lungs.*--Breathing as naturally as
possible, expel the air into a spirometer (lung tester) during a period,
say of ten respirations (Fig. 53). Note the total amount of air exhaled
and the number of "breaths" and calculate the amount of air exhaled at
each breath. This is called the _tidal_ air.
[Fig. 53]
Fig. 53--*Apparatus* (spirometer) for measuring the capacity of the lungs.
2. After an ordinary inspiration empty the lungs as completely as possible
into the spirometer, noting the quantity exhaled. This amount, less the
tidal air, is known as the _reserve_ air. The air which is now left in the
lungs is called the _residual_ air. On the theory that this is equal in
amount to the reserve air, calculate the capacity of the lungs in an
ordinary inspiration.
3. Now fill the lungs to the full expansion of the chest and empty them as
completely as possible into the spirometer, noting the amount expelled.
This, less the tidal air and the reserve air, is called the _complemental_
air. Now calculate the total capacity of the lungs.
CHAPTER VIII - PASSAGE OF OXYGEN THROUGH THE BODY
What is the nature of oxygen? What is its purpose in the body and how does
it serve this purpose? How is the blood able to take it up at the lungs
and give it off at the cells? What becomes of it after being used? These
are questions touching the maintenance of life and they deserve careful
consideration.
*Nature of Oxygen.*--To understand the relation which oxygen sustains to
the body we must acquaint ourselves with certain of its chemical
properties. It is an element(44) of intense affinity, or combining power,
and is one of the most active of all chemical agents. It is able to
combine with most of the other elements to form chemical compounds. A
familiar example of its combining action is found in ordinary combustion,
or burning. On account of the part it plays in this process, oxygen is
called the _supporter of combustion_; but it supports combustion by the
simple method of uniting. The ashes that are left and the invisible gases
that escape into the atmosphere are the compounds formed by the uniting
process. It thus appears that oxygen, in common with the other elements,
may exist in either of two forms:
1. That in which it is in a _free_, or uncombined, condition--the form in
which it exists in the atmosphere.
2. That in which it is a part of compounds, such as the compounds formed
in combustion.
Oxygen manifests its activity to the best advantage when it is in a free
state, or, more accurately speaking, when it is passing from the free
state into one of combination. It is separated from its compounds and
brought again into a free state by overcoming with heat, or some other
force, the affinity which causes it to unite.
*How Oxygen unites.*--The chemist believes oxygen, as well as all other
substances, to be made up of exceedingly small particles, called _atoms_.
The atoms do not exist singly in either elements or compounds, but are
united with each other to form groups of atoms that are called
_molecules_. In an element the molecules are made up of one kind of atoms,
but in a compound the molecules are made up of as many kinds of atoms as
there are elements in the compound. Changes in the composition of
substances (called chemical changes) are due to rearrangements of the
atoms and the formation of new molecules. The atoms, therefore, are the
units of chemical combination. In the formation of new compounds they
unite, and in the breaking up of existing compounds they separate.
The uniting of oxygen is no exception to this general law. All of its
combinations are brought about by the uniting of its atoms. In the burning
of carbon, for example, the atoms of oxygen and the atoms of carbon unite,
forming molecules of the compound known as carbon dioxide. The chemical
formula of this compound, which is CO_2, shows the proportion in which the
atoms unite--one atom of carbon uniting with two atoms of oxygen in each of
the molecules. The affinity of oxygen for other elements, and the affinity
of other elements for oxygen, and for each other, resides in their atoms.
*Oxidation.*--The uniting of oxygen with other elements is termed
_oxidation_. This may take place slowly or rapidly, the two rates being
designated as _slow_ oxidation and _rapid_ oxidation. Examples of slow
oxidation are found in certain kinds of decay and in the rusting of iron.
Combustion is an example of rapid oxidation. Slow and rapid oxidation,
while differing widely in their effects upon surrounding objects, are
alike in that both produce heat and form compounds of oxygen. In slow
oxidation, however, the heat may come off so gradually that it is not
observed.
*Movement of Oxygen through the Body.*--Oxygen has been shown in the
preceding chapters to pass from the lungs into the blood and later to
leave the blood and, passing through the lymph, to enter the cells. That
oxygen does not become a permanent constituent of the cells is shown by
the constancy of the body weight. Nearly two pounds of oxygen per day are
known to enter the cells of the average-sized person. If this became a
permanent part of the cells, the body would increase in weight from day to
day. Since the body weight remains constant, or nearly so, we must
conclude that oxygen leaves the body about as fast as it enters. Oxygen
enters the body as a _free_ element. The form in which it leaves the body
will be understood when we realize the purpose which it serves and the
method by which it serves this purpose.
*Purpose of Oxygen in the Body.*--The question may be raised: Is it
possible for oxygen to serve a purpose in the body without remaining in
it? This, of course, depends upon what the purpose is. That it is possible
for oxygen to serve a purpose and at the same time pass on through the
place where it serves that purpose, is seen by studying the combustion in
an ordinary stove (Fig. 54). Oxygen enters at the draft and for the most
part passes out at the flue, but in passing through the stove it unites
with, or oxidizes, the fuel, causing the combustion which produces the
heat.
[Fig. 54]
Fig. 54--*Coal stove* illustrating rapid oxidation.
Now it is found that certain chemical processes, mainly oxidations, are
taking place in the body. These produce the heat for keeping it warm and
also supply other forms of energy,(45) including motion. It is the purpose
of oxygen to keep up these oxidations and, by so doing, to aid in
supplying the body with energy. It serves this purpose in much the same
way that it supports combustion, _i.e._, by uniting with, or oxidizing,
materials derived from foods that are present in the cells.
*Does Oxygen serve Other Purposes?*--It has been suggested that oxygen may
serve the purpose of oxidizing, or destroying, substances that are
injurious and of acting, in this way, as a purifying agent in the body. In
support of this view is the natural tendency of oxygen to unite with
substances and the well-known fact that oxygen is an important natural
agent in purifying water. It seems probable, therefore, that it may to a
slight extent serve this purpose in the body. It is probable also that
oxygen aids through its chemical activity in the formation of compounds
which are to become a part of the cells. Both of these uses, however, are
of minor importance when compared with _the main use of oxygen_, which _is
that of an aid in supplying energy to the body_.
*Oxygen and the Maintenance of Life.*--In the supplying of energy to the
body, one of the conditions necessary to the maintenance of life is
provided. Because oxygen is necessary to this process, and because death
quickly results when the supply of it is cut off, oxygen is frequently
called the supporter of life. This idea is misleading, for oxygen has no
more to do with the maintenance of life than have the food materials with
which it unites. Life appears to be more dependent upon oxygen than upon
food, simply because the supply of it in the body at any time is
exceedingly small. Being continually surrounded by an atmosphere
containing free oxygen, the body depends upon this as a constant source of
supply, and does not store it up. Food, on the other hand, is taken in
excess of the body's needs and stored in the various tissues, the supply
being sufficient to last for several days. When the supply of either
oxygen or food is exhausted in the body, life must cease.
*The Oxygen Movement a Necessity.*--Since _free_ oxygen is required for
keeping up the chemical changes in the cells, and since it ceases to be
free as soon as it goes into combination, its continuous movement through
the body is a necessity. The oxygen compounds must be removed as fast as
formed in order to make room for more free oxygen. This movement has
already been studied in connection with the blood and the organs of
respiration, but the consideration of certain details has been deferred
till now. By what means and in what form is the oxygen passed _to_ and
_from_ the cells?
*Passage of Oxygen through the Blood.*--In serving its purpose at the
cells, the oxygen passes twice through the blood--once as it goes toward
the cells and again as it passes from the cells to the exterior of the
body:
_Passage toward the Cells._--This is effected mainly through the hemoglobin
of the red corpuscles. At the lungs the oxygen and the hemoglobin form a
weak chemical compound that breaks up and liberates the oxygen when it
reaches the capillaries in the tissues. The separation of the oxygen from
the hemoglobin at the tissues appears to be due to two causes: first, to
the weakness of the chemical attraction between the atoms of oxygen and
the atoms that make up the hemoglobin molecule; and second, to a
difference in the so-called _oxygen pressure_ at the lungs and at the
tissues.(46)
The attraction of the oxygen and the hemoglobin is sufficient to cause
them to unite where the oxygen pressure is more than one half pound to the
square inch, but it is not sufficiently strong to cause them to unite or
to prevent their separation, if already united, where the oxygen pressure
is less than one half pound to the square inch. The oxygen pressure at the
lungs, which amounts to nearly three pounds to the square inch, easily
causes the oxygen and the hemoglobin to unite, while the almost complete
absence of any oxygen pressure at the tissues, permits their separation.
The blood in its circulation constantly flows from the place of high
oxygen pressure at the lungs to the place of low oxygen pressure at the
tissues and, in so doing, loads up with oxygen at one place and unloads it
at the other (Fig. 55).
_Passage from the Cells._--Since oxygen leaves the free state at the cells
and becomes a part of compounds, we are able to trace it from the body
only by following the course of these compounds. Three waste compounds of
importance are formed at the cells--carbon dioxide (CO2), water (H2O), and
urea (N2H4CO). The first is formed by the union of oxygen with carbon, the
second by its union with hydrogen, and the third by its union with
nitrogen, hydrogen, and carbon. These compounds are carried by the blood
to the organs of excretion, where they are removed from the body. The
water leaves the body chiefly as a liquid, the urea as a solid dissolved
in water, and the carbon dioxide as a gas. The passage of carbon dioxide
through the blood requires special consideration.
[Fig. 55]
Fig. 55--*Diagram illustrating movement, of oxygen and carbon dioxide
through the body* (S.D. Magers). Each moves from a place of relatively
high to a place of relatively low pressure. (See text.)
*Passage of Carbon Dioxide through the Blood.*--Part of the carbon dioxide
is dissolved in the plasma of the blood, and part of it is in weak
chemical combination with substances found in the plasma and in the
corpuscles. Its passage through the blood is accounted for in the same way
as the passage of the oxygen. Its ability to dissolve in liquids and to
enter into chemical combination varies as the _carbon dioxide
pressure_(47) This in turn varies with the amount of the carbon dioxide,
which is greatest at the cells (where it is formed), less in the blood,
and still less in the lungs. Because of these differences, the blood is
able to take it up at the cells and release it at the lungs (Fig. 55).
[Fig. 56]
Fig. 56--*Soap bubble* floating in a vessel of carbon dioxide, illustrating
the difference in weight between air and carbon dioxide gas.
*Properties of Carbon Dioxide.*--Carbon dioxide is a colorless gas with
little or no odor. It is classed as a heavy gas, being about one third
heavier than air(48) (Fig. 56). It does not support combustion, but on the
contrary is used to some extent to extinguish fires. It is formed by the
oxidation of carbon in the body, and by the combustion of carbon outside
of the body. It is also formed by the decay of animal and vegetable
matter. From these sources it is continually finding its way into the
atmosphere. Although not a poisonous gas, carbon dioxide may, if it
surround the body, shut out the supply of oxygen and cause death.(49)
*Final Disposition of Carbon Dioxide.*--It is readily seen that the union
of carbon and oxygen, which is continually removing oxygen from the air
and replacing it with carbon dioxide, tends to make the whole atmosphere
deficient in the one and to have an excess of the other. This tendency is
counteracted through the agency of vegetation. Green plants absorb the
carbon dioxide from the air, decompose it, build the carbon into compounds
(starch, etc.) that become a part of the plant, and return the free oxygen
to the air (Fig. 57). In doing this, they not only preserve the necessary
proportion of oxygen and carbon dioxide in the atmosphere, but also put
the carbon and oxygen in such a condition that they can again unite. The
force which enables the plant cells to decompose the carbon dioxide is
supplied by the sunlight (Chapter XII).
[Fig. 57]
Fig. 57--*Under surface* of a geranium leaf showing breathing pores, highly
magnified (O.H.).
*Summary.*--Oxygen, by uniting with materials at the cells, keeps up a
condition of chemical activity (oxidation) in the body. This supplies heat
and the other forms of bodily energy. Entering as a free element, oxygen
leaves the body as a part of the waste compounds which it helps to form.
The free oxygen is transported from the lungs to the cells by means of the
hemoglobin of the red corpuscles, while the combined oxygen in carbon
dioxide and other compounds from the cells is carried mainly by the
plasma. The limited supply of free oxygen in the body at any time makes
necessary its continuous introduction into the body.
*Exercises.*--1. Describe the properties of oxygen. How does it unite with
other elements? How does it support combustion?
2. State the purpose of oxygen in the body. What properties enable it to
fulfill this purpose?
3. What is the proof that oxygen does not remain permanently in the body?
How does the oxygen entering the body differ from the same oxygen as it
leaves the body?
4. What is the necessity for the _continuous_ introduction of oxygen into
the body, while food is introduced only at intervals?
5. How are the red corpuscles able to take up and give off oxygen? How is
the plasma able to take up and give off carbon dioxide?
6. If thirty cubic inches of air pass from the lungs at each expiration
and 4.5 per cent of this is carbon dioxide, calculate the number of cubic
feet of the gas expelled in twenty-four hours, estimating the number of
respirations at eighteen per minute.
7. What is the weight of this volume of carbon dioxide, if one cubic foot
weigh 1.79 ounces?
8. What portion of this weight is oxygen and what carbon, the ratio by
weight of carbon to oxygen in carbon dioxide being twelve to thirty-two?
9. What is the final disposition of carbon dioxide in the atmosphere?
PRACTICAL WORK
*To show the Difference between Free Oxygen and Oxygen in
Combination.*--Examine some crystals of potassium chlorate (KClO3). They
contain oxygen _in combination_ with potassium and chlorine. Place a few
of these in a small test tube and heat strongly in a gas or alcohol flame.
The crystals first melt, and the liquid which they form soon appears to
boil. If a splinter, having a spark on the end, is now inserted in the
tube, it is kindled into a flame. This shows the presence of _free_
oxygen, the heat having caused the potassium chlorate to decompose. The
difference between free and combined oxygen may also be shown by
decomposing other compounds of oxygen, such as water and mercuric oxide.
*Preparation and Properties of Oxygen.*--Intimately mix 3 grams (1/2
teaspoonful) of potassium chlorate with half its bulk of manganese
dioxide, and place the mixture in a large test tube. Close the test tube
with a tight-fitting stopper which bears a glass tube of sufficient length
and of the right shape to convey the escaping gas to a small trough or pan
partly filled with water, on the table. Fill four large-mouthed bottles
with water and, by covering with cardboard, invert each in the trough of
water. Arrange the test tube conveniently for heating, letting the end of
the glass tube terminate under the mouth of one of the bottles (Fig. 58).
Using an alcohol lamp or a Bunsen burner, heat over the greater portion of
the tube at first, but gradually concentrate the flame upon the mixture.
Do not heat too strongly, and when the gas is coming off rapidly, remove
the flame entirely, putting it back as the action slows down. After all
the bottles have been filled, remove the end of the glass tube from the
water, but leave the bottles of oxygen inverted in the trough until they
are to be used. On removing the bottles from the trough, keep the tops
covered with wet cardboard.
[Fig. 58]
Fig. 58--*Apparatus* for generating oxygen.
1. Examine a bottle of oxygen, noting its lack of color. Insert a small
burning splinter in the upper part of the bottle and observe the change in
the rate of burning. The air contains free oxygen, but it is diluted with
nitrogen. Compare this with the undiluted oxygen in the bottle as to
effect in causing the splinter to burn.
2. In a second bottle of oxygen insert a splinter without the flame, but
having a small spark on the end. As soon as the oxygen kindles the spark
into a flame, withdraw from the bottle and blow out the flame, but again
insert the spark. Repeat the experiment as long as the spark is kindled by
the oxygen into a flame. This experiment is usually performed as a test
for undiluted oxygen.
3. Make a hollow cavity in the end of a short piece of crayon. Fasten a
wire to the crayon, and fill the cavity with powdered sulphur. Ignite the
sulphur in the flame of an alcohol lamp or Bunsen burner, and lower it
into a bottle of oxygen. Observe the change in the rate of burning, the
color of the flame, and the material formed in the bottle by the burning.
The gas remaining in the bottle is sulphur dioxide (SO2), formed by the
_uniting_ of the sulphur and the oxygen.
4. Bend a small loop on the end of a piece of picture wire. Heat the loop
in a flame and insert it in some powdered sulphur. Ignite the melted
sulphur which adheres, and insert it quickly in a bottle of oxygen.
Observe the dark, brittle material which is formed by the burning of the
iron. It is a compound of the iron with oxygen, similar to iron rust, and
formed by their uniting.
*Preparation and Properties of Carbon Dioxide.*--1. (_a_) Attach a piece of
carbon (charcoal) no larger than the end of the thumb to a piece of wire.
Ignite the charcoal in a hot flame and lower it into a vessel of oxygen.
Observe its combustion, letting it
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