The Dancing Mouse: A Study in Animal Behavior
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Title: The Dancing Mouse: A Study in Animal Behavior
Author: Robert Mearns Yerkes
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*** START OF THE PROJECT GUTENBERG EBOOK THE DANCING MOUSE: A STUDY IN ANIMAL BEHAVIOR ***
Produced by Juliet Sutherland, Michael Oltz,
Charles Franks and the Online Distributed Proofreading Team.
[Illustration: DANCING MICE--SNIFFING AND EATING.]
THE ANIMAL BEHAVIOR SERIES. VOLUME I
THE DANCING MOUSE
A Study in Animal Behavior
BY
ROBERT M. YERKES, Ph.D.
INSTRUCTOR IN COMPARATIVE PSYCHOLOGY IN HARVARD
UNIVERSITY
The Cartwright Prize of the Alumni Association of the College of
Physicians and Surgeons, Columbia University, was awarded, in 1907, for an
Essay which comprised the first twelve chapters of this volume.
1907
IN LOVE AND GRATITUDE
THIS BOOK IS DEDICATED TO
MY MOTHER
PREFACE
This book is the direct result of what, at the time of its occurrence,
seemed to be an unimportant incident in the course of my scientific work--
the presentation of a pair of dancing mice to the Harvard Psychological
Laboratory. My interest in the peculiarities of behavior which the
creatures exhibited, as I watched them casually from day to day, soon
became experiment-impelling, and almost before I realized it, I was in the
midst of an investigation of their senses and intelligence.
The longer I observed and experimented with them, the more numerous became
the problems which the dancers presented to me for solution. From a study
of the senses of hearing and sight I was led to investigate, in turn, the
various forms of activity of which the mice are capable; the ways in which
they learn to react adaptively to new or novel situations; the facility
with which they acquire habits; the duration of habits; the roles of the
various senses in the acquisition and performance of certain habitual
acts; the efficiency of different methods of training; and the inheritance
of racial and individually acquired forms of behavior.
In the course of my experimental work I discovered, much to my surprise,
that no accurate and detailed account of this curiously interesting animal
existed in the English language, and that in no other language were all
the facts concerning it available in a single book. This fact, in
connection with my appreciation of the exceptional value of the dancer as
a pet and as material for the scientific study of animal behavior, has led
me to supplement the results of my own observation by presenting in this
little book a brief and not too highly technical description of the
general characteristics and history of the dancer.
The purposes which I have had in mind as I planned and wrote the book are
three: first, to present directly, clearly, and briefly the results of my
investigation; second, to give as complete an account of the dancing mouse
as a thorough study of the literature on the animal and long-continued
observation on my own part should make possible; third, to provide a
supplementary text-book on mammalian behavior and on methods of studying
animal behavior for use in connection with courses in Comparative
Psychology, Comparative Physiology, and Animal Behavior.
It is my conviction that the scientific study of animal behavior and of
animal mind can be furthered more just at present by intensive special
investigations than by extensive general books. Methods of research in
this field are few and surprisingly crude, for the majority of
investigators have been more deeply interested in getting results than in
perfecting methods. In writing this account of the dancing mouse I have
attempted to lay as much stress upon the development of my methods of work
as upon the results which the methods yielded. In fact, I have used the
dancer as a means of exhibiting a variety of methods by which the behavior
and intelligence of animals may be studied. As it happens the dancer is an
ideal subject for the experimental study of many of the problems of animal
behavior. It is small, easily cared for, readily tamed, harmless,
incessantly active, and it lends itself satisfactorily to a large number
of experimental situations. For laboratory courses in Comparative
Psychology or Comparative Physiology it well might hold the place which
the frog now holds in courses in Comparative Anatomy.
Gratefully, and with this expression of my thanks, I acknowledge my
indebtedness to Professor Hugo Münsterberg for placing at my command the
resources of the Harvard Psychological Laboratory and for advice and
encouragement throughout my investigation; to Professor Edwin B. Holt for
valuable assistance in more ways than I can mention; to Professor Wallace
C. Sabine for generous aid in connection with the experiments on hearing;
to Professor Theobald Smith for the examination of pathological dancers;
to Miss Mary C. Dickerson for the photographs of dancing mice which are
reproduced in the frontispiece; to Mr. Frank Ashmore for additional
photographs which I have been unable to use in this volume; to Mr. C. H.
Toll for the drawings for Figures 14 and 20; to Doctors H. W. Rand and C.
S. Berry for valuable suggestions on the basis of a critical reading of
the proof sheets; and to my wife, Ada Watterson Yerkes, for constant aid
throughout the experimental work and in the preparation of this volume.
R. M. Y.
CAMBRIDGE, MASSACHUSETTS,
August, 1907.
CONTENTS
LIST OF ILLUSTRATIONS
LITERATURE ON THE DANCING MOUSE
CHAPTER I
CHARACTERISTICS, ORIGIN, AND HISTORY
Peculiarities of the dancing mouse--Markings and method of keeping record
of individuals--The dancer in China and Japan (Kishi, Mitsukuri, Hatai)--
Theories concerning the origin of the race: selectional breeding; the
inheritance of an acquired character; mutation, inheritance, and
selectional breeding; pathological changes; natural selection--Instances
of the occurrence of dancers among other kinds of mice--Results of
crossing dancer with other kinds of mice.
CHAPTER II
FEEDING, BREEDING, AND DEVELOPMENT OF THE YOUNG
Methods of keeping and caring for dancers--Cages, nest-boxes, and
materials for nest--Cleansing cages--Food supply and feeding--Importance
of cleanliness, warmth, and pure food--Relations of males and females,
fighting--The young, number in a litter--Care of young--Course of
development--Comparison of young of dancer with young of common mouse--
Diary account of the course of development of a typical litter of dancers.
CHAPTER III
BEHAVIOR: DANCE MOVEMENTS
Dancing--Restlessness and excitability--Significance of restlessness--
Forms of dance: whirling, circling, and figure-eights--Direction of
whirling and circling: right whirlers, left whirlers, and mixed whirlers--
Sex differences in dancing--Time and periodicity of dancing--Influence of
light on activity--Necessity for prolonged observation of behavior.
CHAPTER IV
BEHAVIOR: EQUILIBRATION AND DIZZINESS
Muscular coordination--Statements of Cyon and Zoth concerning behavior--
Control of movements, orientation, equilibration, movement on inclined
surfaces, climbing--The tracks of the dancer--Absence of visual
dizziness--Comparison of the behavior of the dancer with that of the
common mouse when they are rotated in a cyclostat--Behavior of blinded
dancers (Cyon, Alexander and Kreidl, Kishi)--Cyon's two types of dancer--
Phenomena of behavior for which structural bases are sought: dance
movements; lack of response to sounds; deficiency in equilibrational
ability; lack of visual and rotational dizziness.
CHAPTER V
STRUCTURAL PECULIARITIES AND BEHAVIOR
The functions of the ear--Structure of the ear of the dancer as described
by Rawitz, by Panse, by Baginsky, by Alexander and Kreidl, and by Kishi--
Cyon's theory of the relation of the semicircular canals to space
perception--Condition of the auditory organs--Condition of the
equilibrational organs--Condition of the sound-transmitting organs--The
bearing of the results of anatomical investigations upon the facts of
behavior.
CHAPTER VI
THE SENSE OF HEARING
Experiments on hearing in the dancer made by Rawitz, by Panse, by Cyon, by
Alexander and Kreidl, by Zoth, and by Kishi--Hearing and the voice--
Methods of testing sensitiveness to sounds--Results of tests with adults--
Importance of indirect method of experimentation--Results of tests with
young--The period of auditory sensitiveness--Individual differences.
CHAPTER VII
THE SENSE OF SIGHT: BRIGHTNESS VISION
What is known concerning sight in the dancer--Brightness vision and color
vision--Methods of testing brightness vision, the visual discrimination
apparatus--Motives for discrimination and choice--Punishment versus reward
as an incentive in animal experiments--Hunger as an incentive--An electric
stimulus as an incentive--Conditions for brightness vision tests--
White-black vision--Evidence of preference--Check experiments--Conclusion.
CHAPTER VIII
THE SENSE OF SIGHT: BRIGHTNESS VISION (_Continued_)
The delicacy of brightness discrimination--Methods of testing the dancer's
ability to detect slight differences in brightness--Results of tests with
gray papers--Relation of intensity of visual stimuli to the threshold of
discrimination--Weber's law apparatus and method of experimentation--
Results of Weber's law tests--Practice effects, the training of vision--
Description of the behavior of the dancer in the discrimination box
experiments--Modes of choice: by affirmation; by negation; by comparison--
Evidence of indiscriminable visual conditions.
CHAPTER IX
THE SENSE OF SIGHT: COLOR VISION
Does the dancer see colors?--The food-box method of testing color vision--
Waugh's food-box method--Results of tests--Tests by the use of colored
papers in the visual discrimination box--Yellow-red vision--Blue-orange
vision--Brightness vision _versus_ color vision--Brightness check
tests--Green-blue vision--Violet-red vision--Conclusions.
CHAPTER X
THE SENSE OF SIGHT: COLOR VISION (_Continued_)
The use of color filters--Testing color vision by the use of transmitted
light--Green-blue vision--Green-red vision--Blue-red vision--Stimulating
value of different portions of the spectrum--Does red appear darker to the
dancer than to us?--Conclusions concerning color vision--Structure of the
retina of the dancer and its significance.
CHAPTER XI
THE ROLE OF SIGHT IN THE DAILY LIFE OF THE DANCER.
Sight and general behavior--Behavior of blinded dancers--Experimental
tests of ability to perceive form--Visual guidance in mazes--Following
labyrinth paths in the dark--The relative importance of visual, olfactory,
and kinaesthetic stimuli--Conditions for the acquisition of a motor
habit--Conditions for the execution of an habitual act.
CHAPTER XII
EDUCABILITY: METHODS OF LEARNING
The modifiability of behavior--Educational value of experimental studies
of modifiability--Methods: the problem method; the labyrinth method; the
discrimination method--Relation of method to characteristics of animal--
Simple test of the docility of the dancer--Lack of imitative tendency--
Persistence of useless acts--Manner of profiting by experience--Individual
differences in initiative.
CHAPTER XIII
HABIT FORMATION: THE LABYRINTH HABIT
The labyrinth method--Problems--Preliminary tests--Comparison of the
behavior of the dancer in a maze with that of the common mouse--Evolution
of a labyrinth method--Records of time and records of errors--Simple and
effective method of recording the path--Curves of habit formation--Regular
and irregular labyrinths--Points for a standard labyrinth--Values and
defects of the labyrinth method.
CHAPTER XIV
HABIT FORMATION: THE DISCRIMINATION METHOD
Quantitative _versus_ qualitative results--Motives--Precautions--
Preference--Results of systematic habit-forming experiments--Curves of
habit formation--Meaning of irregularity in curve--Individual
differences--Comparison of curves for discrimination habits with those for
labyrinth habits--Averages--The index of modifiability as a measure of
docility--Reliability of the index.
CHAPTER XV
THE EFFICIENCY OF TRAINING METHODS
Importance of measuring the efficiency of educational methods--Rapidity of
learning and permanency of modifications wrought by training--Results of a
study of the efficiency of discrimination methods--Comparison by means of
indices of modifiability--Number of tests per series versus number of
series--Efficiency as measured by memory tests.
CHAPTER XVI
THE DURATION OF HABITS: MEMORY AND RE-LEARNING
Measures of the permanency of modifications in behavior--The duration of
brightness and color discrimination habits--The relation of learning to
re-learning--Can a habit which has been lost completely be re-acquired
with greater facility than it was originally acquired?--Relation of
special training to general efficiency--Does the training in one form of
labyrinth aid the dancer in acquiring other labyrinth habits?
CHAPTER XVII
INDIVIDUAL, AGE, AND SEX DIFFERENCES IN BEHAVIOR
Individual peculiarities in sensitiveness, docility, and initiative--The
relation of docility to age--The individual result and the average--How
averages conceal facts--Sex differences in docility and initiative--
Individual differences of motor capacity which seem to indicate
varieties--Is the dancer pathological?
CHAPTER XVIII
THE INHERITANCE OF FORMS OF BEHAVIOR
Characteristics of the race--Inheritance of the tendency to whirl in a
particular way--Tests of the inheritance of individually acquired forms of
behavior.
INDEX
ILLUSTRATIONS
Dancing Mice--sniffing and eating _Frontispiece_
FIGURE
1. Color patterns of dancers. Record blanks
2. Double cage, with nest-boxes and water dishes
3. Double cages in frame
4. Photographs of dancers climbing (After Zoth)
5. Tracks of common mouse (After Alexander and Kreidl)
6. Tracks of dancer (After Alexander and Kreidl)
7. The inner ear of the rabbit (Retzius)
8. The membranous labyrinth of the ear of the dancer (After Rawitz)
9. Same
10. Same
it. Model of the ear of the dancer (After Baginsky)
12. Ear of the dancer (After Kishi)
13. Ear of the dancer (After Kishi)
14. Discrimination box
15. Ground plan of discrimination box
16. Nendel's gray papers
17. Weber's law apparatus
18. Food-box apparatus
19. Waugh's food-box apparatus
20. Color discrimination apparatus
21. Ground plan of color discrimination apparatus
22. Cards for form discrimination
23. Labyrinth B
24. Labyrinth B on electric wires
25. Labyrinth A
26. Curves of habit formation for labyrinth B
27. Plan of labyrinth C, and path records
28. Labyrinth D
29. Curve of learning for white-black discrimination, twenty individuals
30. Curve of learning for white-black discrimination, thirty individuals
31. Curve of habit formation for labyrinth D
32. Curves of learning and re-learning
33. Plasticity curves
LITERATURE ON THE DANCING MOUSE
1. ALEXANDER, G. UND KREIDL, A. "Zur Physiologie des Labyrinths der
Tanzmaus." _Archiv für die gesammte Physiologie_, Bd. 82: 541-552.
1900.
2. ALEXANDER, G. UND KREIDL, A. "Anatomisch-physiologische Studien über
das Ohrlabyrinth der Tanzmaus." II Mittheilung. _Archiv für die gesammte
Physiologie_. Bd. 88: 509-563. 1902.
3. ALEXANDER, G. UND KREIDL, A. "Anatomisch-physiologische Studien über
das Ohrlabyrinth der Tanzmaus." III Mittheilung. _Archiv für die
gesammte Physiologie_, Bd. 88: 564-574. 1902.
4. BAGINSKY, B. "Zur Frage über die Zahl der Bogengänge bei japanischen
Tanzmäusen." _Centralblatt für Physiologie_, Bd. 16: 2-4. 1902.
5. BATESON, W. "The present state of knowledge of colour-heredity in mice
and rats." _Proceedings of the Zoölogical Society of London_, Vol. 2:
71-99. 1903.
6. BREHM, A. E. "Tierleben." Dritte Auflage. Saugetiere, Bd. 2: 513-514.
1890.
7. BREHM, A. E. "Life of Animals." Translated from the third German
edition of the "Tierleben" by G. R. Schmidtlein. Mammalia, p. 338.
Marquis, Chicago. 1895.
8. CYON, E. DE. "Le sens de l'espace chez les souris dansantes
japonaises." _Cinquantenaire de la Société de Biologie_ (Volume
jubilaire). p. 544-546. Paris. 1899.
9. CYON, E. VON. "Ohrlabyrinth, Raumsinn und Orientirung." _Archiv für
die gesammte Physiologie_, Bd. 79: 211-302. 1900.
10. CYON, E. DE. "Presentation de souris dansantes japonaises." _Comptes
rendus du XIII Congrès International de Paris, Section de
physiologie_, p. 160-161. 1900.
11. CYON, E. VON. "Beiträge zur Physiologie des Raumsinns." I Theil. "Neue
Beobachtungen an den japanischen Tanzmäusen." _Archiv für die gesammte
Physiologie_, Bd. 89: 427-453. 1902.
12. CYON, E. DE. "Le sens de l'espace." Richet's "Dictionnaire de
physiologie," T. 5: 570-571. 1901.
13. DARBISHIRE, A. D. Note on the results of crossing Japanese waltzing
mice with European albino races. _Biometrica_, Vol. 2: 101-104. 1902.
14. DARBISHIRE, A. D. Second report on the result of crossing Japanese
waltzing mice with European albino races. _Biometrica_, Vol.2:
165-173. 1903.
15. DARBISHIRE, A. D. Third report on hybrids between waltzing mice and
albino races. _Biometrica_, Vol. 2: 282-285. 1903.
16. DARBISHIRE, A. D. On the result of crossing Japanese waltzing with
albino mice. _Biometrica_, Vol 3: 1-51. 1904.
17. GUAITA, G. v. "Versuche mit Kreuzungen von verschiedenen Rassen der
Hausmaus." _Berichte der naturforschenden Gesellschaft zu Freiburg i.
B_., Bd. 10: 317-332. 1898.
18. GUAITA, G. v. "Zweite Mitteilung uber Versuche mit Kreuzungen von
verschiedenen Hausmausrassen." _Berichte der naturforschenden
Gesellschaft zu Freiburg i. B_., Bd. 11: 131-138. 1900.
19. HAACKE, W. "Ueber Wesen, Ursachen und Vererbung von Albinismus und
Scheckung und über deren Bedeutung für vererbungstheoretische und
entwicklungsmechanische Fragen." _Biologisches Centralblatt_, Bd.
15: 44-78. 1895.
19a. HUNTER, M. S. "A Pair of Waltzing Mice." _The Century Magazine_,
Vol. 73: 889-893. April, 1907.
20. KAMMERER, P. "Tanzende Waldmaus und radschlagende Hausmaus."
_Zoölogische Garten_, Bd. 41: 389-390. 1900.
21. KISHI, K. "Das Gehörorgan der sogenannten Tanzmaus." _Zeitschrift
für wissenschaftliche Zoölogie_, Bd. 71: 457-485. 1902.
22. LANDOIS, H. "Chinesische Tanzmäuse." _Jahresbericht des Westfähschen
Provinzial-Vereins_, Munster, 1893-1894: 62-64.
22a. LOSE, J. "Waltzing Mice." _Country Life in America_, September,
1904. p. 447.
23. PANSE, R. Zu Herrn Bernhard Rawitz' Arbeit: "Das Gehörorgan der
japanischen Tanzmäuse." _Archiv für Anatomie und Physiologie_,
Physiologische Abtheilung, 1901: 139-140.
24. PANSE, R. "Das Gleichgewichts- und Gehörorgan der japanischen
Tanzmäuse." _Münchener medicinische Wochenschrift_, Jahrgang 48, Bd.
I: 498-499. 1901.
25. RAWITZ, B. "Das Gehörorgan der japanischen Tanzmäuse." _Archiv für
Anatomie und Physiologie_, Physiologische Abtheilung, 1899: 236-243.
26. RAWITZ, B. "Neue Beobachtungen über das Gehörorgan japanischer
Tanzmäuse." _Archiv für Anatomie und Physiologie_, Physiologische
Abtheilung, 1901, Supplement: 171-176.
27. RAWITZ, B. "Zur Frage über die Zahl der Bogengänge bei japanischen
Tanzmäusen." _Centralblatt für Physiologie_, Bd. 15: 649-651. 1902.
28. SAINT-LOUP, R. "Sur le mouvement de manège chez les souris."
_Bulletin de la Société Zoölogique de France_, T. 18: 85-88. 1893.
29. SCHLUMBERGER, C. "A propos d'un netzukè japonais." _Memoires de la
Société Zoölogique de France_, T. 7: 63-64. 1894.
30. WELDON, W. F. R. Mr. Bateson's revisions of Mendel's theory of
heredity. _Biometrica_, Vol. 2: 286-298. 1903.
31. ZOTH, O. "Ein Beitrag zu den Beobachtungen und Versuchen an
japanischen Tanzmäusen." _Archiv für die gesammte Physiologie_, Bd.
86: 147-176. 1901.
32. ANONYMOUS. "Fancy Mice: Their Varieties, Management, and Breeding."
Fourth edition. London: L. Upcott Gill. No date.
CHAPTER I
CHARACTERISTICS, ORIGIN, AND HISTORY
The variety of mouse which is known as the Japanese dancing or waltzing
mouse has been of special interest to biologists and to lovers of pets
because of its curious movements. Haacke in Brehm's "Life of Animals" (7
p. 337)[1] writes as follows concerning certain mice which were brought to
Europe from China and Japan: "From time to time a Hamburg dealer in
animals sends me two breeds of common mice, which he calls Chinese
climbing mice (Chinesische Klettermäuse) and Japanese dancing mice
(Japanische Tanzmäuse). It is true that the first are distinguished only
by their different colors, for their climbing accomplishments are not
greater than those of other mice. The color, however, is subject to many
variations. Besides individuals of uniform gray, light yellow, and white
color, I have had specimens mottled with gray and white, and blue and
white. Tricolored mice seem to be very rare. It is a known fact that we
also have white, black, and yellow mice and occasionally pied ones, and
the Chinese have profited by these variations of the common mouse also, to
satisfy their fancy in breeding animals. The Japanese, however, who are no
less enthusiastic on this point, know how to transform the common mouse
into a really admirable animal. The Japanese dancing mice, which perfectly
justify their appellation, also occur in all the described colors. But
what distinguishes them most is their innate habit of running around,
describing greater or smaller circles or more frequently whirling around
on the same spot with incredible rapidity. Sometimes two or, more rarely,
three mice join in such a dance, which usually begins at dusk and is at
intervals resumed during the night, but it is usually executed by a single
individual."
[Footnote 1: The reference numbers, of which 7 is an example, refer to the
numbers in the bibliographic list which precedes this chapter.]
As a rule the dancing mouse is considerably smaller than the common mouse,
and observers agree that there are also certain characteristic
peculiarities in the shape of the head. One of the earliest accounts of
the animal which I have found, that of Landois (22 p. 62), states,
however, that the peculiarities of external form are not remarkable.
Landois further remarks, with reason, that the name dancing mouse is ill
chosen, since the human dance movement is rather a rhythmic hopping motion
than regular movement in a circle. As he suggests, they might more
appropriately be called "circus course mice" (22 p. 63).
Since 1903 I have had under observation constantly from two to one hundred
dancing mice. The original pair was presented to the Harvard Psychological
Laboratory by Doctor A.G. Cleghorn of Cambridge. I have obtained
specimens, all strikingly alike in markings, size, and general behavior,
from animal dealers in Washington, Philadelphia, and Boston. Almost all of
the dancers which I have had, and they now number about four hundred, were
white with patches, streaks, or spots of black. The black markings
occurred most frequently on the neck, ears, face, thighs, hind legs, about
the root of the tail, and occasionally on the tail itself. In only one
instance were the ears white, and that in the case of one of the offspring
of a male which was distinguished from most of his fellows by the
possession of one white ear. I have had a few individuals whose markings
were white and gray instead of white and black.
The method by which I was able to keep an accurate record of each of my
dancers for purposes of identification and reference is illustrated in
Figure 1. As this method has proved very convenient and satisfactory, I
may briefly describe it. With a rubber stamp[1] a rough outline of a
mouse, like that of Figure 1 A, was made in my record book. On this
outline I then indicated the black markings of the individual to be
described. Beside this drawing of the animal I recorded its number,
sex,[2] date of birth, parentage, and history. B, C, and D of Figure 1
represent typical color patterns. D indicates the markings of an
individual whose ears were almost entirely white. The pattern varies so
much from individual to individual that I have had no trouble whatever in
identifying my mice by means of such records as these.
[Footnote 1: For the use of the plate from which this stamp was made, I am
indebted to Professor W.E. Castle, who in turn makes acknowledgment to
Doctor G.M. Allen for the original drawing.]
[Footnote 2: I have found it convenient to use the even numbers for the
males and the odd numbers for the females. Throughout this book this usage
is followed. Wherever the sex of an individual is not specially given, the
reader therefore may infer that it is a male if the number is even; a
female if the number is odd.]
All of my dancers had black eyes and were smaller as well as weaker than
the albino mouse and the gray house mouse. The weakness indicated by their
inability to hold up their own weight or to cling to an object curiously
enough does not manifest itself in their dancing; in this they are
indefatigable. Frequently they run in circles or whirl about with
astonishing rapidity for several minutes at a time. Zoth (31 p. 173), who
measured the strength of the dancer in comparison with that of the common
mouse, found that it can hold up only about 2.8 times its own weight,
whereas the common white mouse can hold up 4.4 times its weight. No other
accurate measurements of the strength, endurance, or hardiness of the
dancer are available. They are usually supposed to be weak and delicate,
but my own observations cause me to regard them as exceptionally strong in
certain respects and weak in others.
[Illustration: FIGURE I.--Typical markings of dancers. A, blank outline of
mouse for record. B, markings of No. 2 [symbol for male], born September
7, 1905, of unknown parents, died March 30,1907. C, markings of No 43
[symbol for female], born November 10, 1906, of 212 and 211. D,
markings of No. 151 [symbol for female], born February 28, 1906, of 1000
and 5, died February 26, 1907.]
What the Japanese have to say about the dancing mouse is of special
importance because Japan is rather commonly supposed to be its home. For
this reason, as well as because of the peculiar interest of the facts
mentioned, I quote at length from Doctor Kishi (21 p. 457). "The dancing
mouse has received in Europe this name which it does not bear in its own
home, because of the fact that the circular movements which it makes are
similar to the European (human) dance. Sometimes it is also called the
Japanese or Chinese mouse; originally, however, China must have been its
home, since in Japan it is mostly called '_Nankin nesumi_,' the mouse from
Nankin. When this animal came from China to Japan I shall inquire at a
later opportunity. There were originally in Japan two different species of
mouse, the gray and the white; therefore in order to distinguish our
dancing mouse from these it was necessary to use the name of its native
city.
"In Japan, as in Europe, the animal lives as a house animal in small
cages, but the interest which is taken in it there is shown in quite
another way than in Europe, where the whirling movements, to which the
name dancing mouse is due, are of chief interest. For this reason in
Europe it is given as much room as possible in its cage that it may dance
conveniently. In Japan also the circular movements have been known for a
long time, but this has had no influence upon our interest in the animal,
for the human fashion of dancing with us is quite different from that in
Europe. What has lent interest to the creature for us are its prettiness,
its cleverness in tricks, and its activity. It is liked, therefore, as an
amusement for children. For this purpose it is kept in a small cage,
usually fifteen centimeters square, sometimes in a somewhat broader wooden
box one of whose walls is of wire netting. In this box are built usually a
tower, a tunnel, a bridge, and a wheel. The wheel is rather broad, being
made in the form of a drum and pierced with holes on one side through
which the animal can slip in and out. Running around on the inside, the
mouse moves the wheel often for hours at a time, especially in the
evening. Moreover, there are found in the box other arrangements of
different kinds which may be set in motion by the turning of the wheel. No
space remains in the box in which the animal may move about freely, and
therefore one does not easily or often have an opportunity to observe that
the animal makes circular movements, whether voluntarily or involuntarily.
This is the reason that in its home this interesting little animal has
never been studied by any one in this respect."
It is odd indeed that the remarkable capacity of the dancer for the
execution of quick, graceful, dextrous, bizarre, and oft-repeated
movements has not been utilized in America as it has in Japan. The mice
are inexhaustible sources of amusement as well as invaluable material for
studies in animal behavior and intelligence.
Concerning the origin and history of this curious variety of mouse little
is definitely known. I have found no mention of the animal in scientific
literature previous to 1890. The fact that it is called the Chinese
dancing mouse, the Japanese dancing mouse, and the Japanese waltzing mouse
is indicative of the existing uncertainty concerning the origin of the
race.
Thinking that Japanese literature might furnish more information bearing
on the question of racial history than was available from European
sources, I wrote to Professor Mitsukuri of the University of Tokyo, asking
him whether any reliable records of the dancer existed in Japan. He
replied as follows: "I have tried to find what is known in Japan about the
history of the Japanese waltzing mice, but I am sorry to say that the
results are wholly negative. I cannot find any account of the origin of
this freak, either authentic or fictitious, and, strange as it may seem to
you, no study of the mice in a modern sense has been made, so you may
consider the literature on the mouse in the Japanese language as
absolutely _nil_." In explanation of this somewhat surprising ignorance of
the origin of the race in what is commonly supposed to be its native land,
Professor Mitsukuri adds: "The breeders of the mice have mostly been
ignorant men to whom writing is anything but easy."
In response to similar inquiries, I received the following letter,
confirmatory of Professor Mitsukuri's statements, from Doctor S. Hatai of
Wistar Institute, Philadelphia: "If I remember rightly the so-called
Japanese dancing mouse is usually called by us _Nankin-nedzumi_. _Nankin_
means anything which has been imported from China, and _nedzumi_ means
rat-like animal, or in this case mouse, or Chinese mouse. I referred to
one of the standard Japanese dictionaries and found the following
statement: 'The _Nankin-nedzumi_ is one of the varieties of _Mus
spiciosus_ (_Hatszuka-nedzumi_), and is variously colored. It was imported
from China. These mice are kept in cages for the amusement of children,
who watch their play.' _Mus spiciosus_, if I remember correctly, is very
much like _Mus musculus_ in color, size, and several other
characteristics, if not the same altogether."
In Swinhoe's list of the mammals of China, which appeared in the
_Proceedings of the Zoological Society of London_ for 1870, _Mus musculus
L_. is mentioned as occurring in houses in South China and in Formosa. It
is further stated that black and white varieties which are brought from
the Straits are often kept by the Chinese (p. 637).
The statements of Kishi, Mitsukuri, and Hatai which have been quoted,
taken in connection with the opinions expressed by various European
scientists who have studied the dancer, make it seem highly probable that
the race appeared first in China, and was thence introduced into Japan,
from which country it has been brought to Europe and America. Accepting
for the present this conclusion with reference to the place of origin of
the dancer, we may now inquire, how and when did this curious freak, as
Professor Mitsukuri has called it, come into existence? Concerning these
matters there is wide divergence of opinion.
Haacke (6 p. 514), as quoted in Brehm's "Tierleben," says that an animal
dealer with whom he discussed the question of the possible origin of the
dancer maintained that it came from Peru, where it nests in the full
cotton capsules, arranging the cotton fibers in the form of a nest by
running about among them in small circles. Hence the name cotton mouse is
sometimes applied to it. Haacke himself believes, however, that the race
originated either in China or Japan as the result of systematic
selectional breeding. Of this he has no certainty, for he states that he
failed to find any literature on the "beautiful mice of China and Japan."
Whether Haacke's description of the dancing mouse was published elsewhere
previous to its appearance in Brehm's "Tierleben" I am unable to state; I
have found nothing written on the subject by him before 1890. Zoth (31 p.
176) also thinks that the race was developed by systematic breeding, or in
other words, that it is a product of the skill of the Asiatic animal
breeders.
Another account of the origin of the race is that accepted by Kishi (21 p.
481) and some other Japanese biologists. It is their belief that the forms
of movement acquired by the individual as the result of confinement in
narrow cages are inherited. Thus centuries of subjection to the conditions
which Kishi has described (p. 6) finally resulted in a race of mice which
breed true to the dance movement. It is only fair to add, although Kishi
does not emphasize the fact, that in all probability those individuals in
which the dancing tendency was most pronounced would naturally be selected
by the breeders who kept these animals as pets, and thus it would come
about that selectional breeding would supplement the inheritance of an
acquired character. Few indeed will be willing to accept this explanation
of the origin of the dancer so long as the inheritance of acquired
characters remains, as at present, unproved.
Still another mode of origin of the mice is suggested by the following
facts. In 1893 Saint Loup (28 p. 85) advanced the opinion that dancing
individuals appear from time to time among races of common mice. The
peculiarity of movement may be due, he thinks, to an accidental nervous
defect which possibly might be transmissible to the offspring of the
exceptional individual. Saint Loup for several months had under
observation a litter of common mice whose quick, jerky, nervous movements
of the head, continuous activity, and rapid whirling closely resembled the
characteristic movements of the true dancers of China. He states that
these mice ran around in circles of from 1 to 20 cm. in diameter. They
turned in either direction, but more frequently to the left, that is,
anticlockwise. At intervals they ran in figure-eights ([Symbol: figure
eight]) as do the true dancers. According to Saint Loup these exceptional
individuals were healthy, active, tame, and not markedly different in
general intelligence from the ordinary mouse. One of these mice produced a
litter of seven young, in which, however, none of the peculiarities of
behavior of the parents appeared.
In view of this proof of the occurrence of dancing individuals among
common mice, Saint Loup believes that the race of dancers has resulted
from the inheritance and accentuation of an "accidental" deviation from
the usual mode of behavior. It is scarcely necessary to say that this
opinion would be of far greater weight had he observed, instead of
postulating, the inheritance of the peculiarities of movement which he has
described. It might be objected, to the first of his so-called facts, that
the litter resulted from the mating of mice which possessed dancer blood.
Until the occurrence of dancers among varieties of mice which are known to
be unmixed with true dancers is established, and further, until the
inheritance of this peculiar deviation from the normal is proved, Saint
Loup's account of the origin of the dancing mouse race must be regarded as
an hypothesis.
The occurrence of dancing individuals among common mice has been recorded
by several other observers. Kammerer (20 p. 389) reports that he found a
litter of young wood mice (_Mus sylvaticus L_.) which behaved much as do
the spotted dancers of China. He also observed, among a lot of true
dancers, a gray individual which, instead of spinning around after the
manner of the race, turned somersaults at frequent intervals. It is
Kammerer's opinion, as a result of these observations, that the black and
white dancers of China and Japan have been produced by selectional
breeding on the basis of this occasional tendency to move in circles.
Among albino mice Rawitz (25 p. 238) has found individuals which whirled
about rapidly in small circles. He states, however, that they lacked the
restlessness of the Chinese dancers. Some shrews (_Sorex vulgaris L_.)
which exhibited whirling movements and in certain other respects resembled
the dancing mouse were studied for a time by Professor Häcker of Freiburg
in Baden, according to a report by von Guaita (17 p. 317, footnote).
Doctor G. M. Allen of Cambridge has reported to me that he noticed among a
large number of mice kept by him for the investigation of problems of
heredity[1] individuals which ran in circles; and Miss Abbie Lathrop of
Granby, Massachusetts, who has raised thousands of mice for the market,
has written me of the appearance of an individual, in a race which she
feels confident possessed no dancer blood, which whirled and ran about in
small circles much as do the true dancers.
[Footnote 1: Allen, G.M. "The Heredity of Coat Color in Mice." Proc. Amer.
Academy, Vol. 40, 59-163, 1904.]
Although it is possible that some of these cases of the unexpected
appearance of individuals with certain of the dancer's peculiarities of
behavior may have been due to the presence of dancer blood in the parents,
it is not at all probable that this is true of all of them. We may,
therefore, accept the statement that dancing individuals now and then
appear in various races of mice. They are usually spoken of as freaks,
and, because of their inability to thrive under the conditions of life of
the race in which they happen to appear, they soon perish.
Another and a strikingly different notion of the origin of the race of
dancers from those already mentioned is that of Cyon (11 p. 443) who
argues that it is not a natural variety of mouse, as one might at first
suppose it to be, but instead a pathological variation. The pathological
nature of the animals is indicated, he points out, by the exceptionally
high degree of variability of certain portions of the body. According to
this view the dancing is due to certain pathological structural conditions
which are inherited. Cyon's belief raises the interesting question, are
the mice normal or abnormal, healthy or pathological? That the question
cannot be answered with certainty off-hand will be apparent after we have
considered the facts of structure and function which this volume presents.
Everything organic sooner or later is accounted for, in some one's mind,
by the action of natural selection. The dancing mouse is no exception, for
Landois (22 p. 62) thinks that it is the product of natural selection and
heredity, favored, possibly, by selectional breeding in China. He further
maintains that the Chinese dancer is a variety of _Mus musculus L._ in
which certain peculiarities of behavior appear because of bilateral
defects in the brain. This author is not alone in his belief that the
brain of the dancer is defective, but so far as I have been able to
discover he is the only scientist who has had the temerity to appeal to
natural selection as an explanation of the origin of the race.
Milne-Edwards, as quoted by Schlumberger (29 p. 63), is of the opinion
that the Chinese dancer is not a natural wild mouse race, but instead the
product of rigid artificial selection. And in connection with this
statement Schlumberger describes a discovery of his own which seems to
have some bearing upon the problem of origin. In an old Japanese wood
carving which came into his possession he found a group of dancing mice.
The artist had represented in minute detail the characteristics of the
members of the group, which consisted of the parents and eight young. The
father and mother as well as four of the little mice are represented as
white spotted with black. Of the four remaining young mice, two are
entirely black and two entirely white. The two pure white individuals have
pink eyes, as has also the mother. The eyes of all the others are black.
From these facts Schlumberger infers that the dancer has resulted from the
crossing of a race of black mice with a race of albinos; the two original
types appear among the offspring in the carving.
Experimental studies of the inheritance of the tendency to dance are of
interest in their bearing upon the question of origin. Such studies have
been made by Haacke (19), von Guaita (17, 18), and Darbishire (13, 14, 15,
16), and the important results of their investigations have been well
summarized by Bateson (5).
By crossing dancing mice with common white mice both Haacke and von Guaita
obtained gray or black mice which are very similar to the wild house mouse
in general appearance and behavior. The characteristic movements of the
dancers do not appear. As the result of a long series of breeding
experiments, Darbishire (16 pp. 26, 27) says: "When the race of waltzing
mice is crossed with albino mice which do not waltz, the waltzing habit
disappears in the resulting young, so that waltzing is completely
recessive in Mendel's sense; the eye-color of the hybrids is always dark;
the coat-color is variable, generally a mixture of wild-gray and white,
the character of the coat being distinctly correlated with characters
transmitted both by the albino and by the colored parent." When hybrids
produced by the cross described by Darbishire are paired, they produce
dancers in the proportion of about one to five.
Bateson (5 p. 93, footnote), in discussing the results obtained by Haacke,
von Guaita, and Darbishire, writes: "As regards the waltzing character,
von Guaita's experiments agree with Darbishire's in showing that it was
always recessive to the normal. No individual in F1 [thus the first hybrid
generation is designated] or in families produced by crossing F1 with the
pure normal, waltzed. In Darbishire's experiments F1 x F1 [first hybrids
mated] gave 8 waltzers in 37 offspring, indicating 1 in 4 as the probable
average. From von Guaita's matings in the form DR x DR the totals of
families were 117 normal and 21 waltzers.... There is therefore a large
excess of normals over the expected 3 to 1. This is possibly due to the
delicacy of the waltzers, which are certainly much more difficult to rear
than normals are. The small number in von Guaita's litters makes it very
likely that many were lost before such a character as this could be
determined."
Bateson does not hazard a guess at the origin of the dancer, but merely
remarks (5 p. 86) that the exact physiological basis of the dancing
character is uncertain and the origin of this curious variation in
behavior still more obscure. "Mouse fanciers have assured me," he
continues, "that something like it may appear in strains inbred from the
normal type, though I cannot find an indubitable case. Such an occurrence
may be nothing but the appearance of a rare recessive form. Certainly it
is not a necessary consequence of inbreeding, witness von Guaita's long
series of inbred albinos." (von Guaita (17 p. 319) inbred for twenty-eight
generations.)
From the foregoing survey of the available sources of information
concerning the origin and history of the race of dancing mice the
following important facts appear. There are four theories of the origin of
the race: (1) origin by selectional breeding (Haacke, Zoth, Milne-
Edwards); (2) origin through the inheritance of an acquired character
(Kishi); (3) origin by mutation, inheritance, and selectional breeding
(Saint Loup, Kammerer, Cyon); (4) origin by natural selection, and
inheritance, favored by selectional breeding (Landois). Everything
indicates that the race originated in China. It is fairly certain that
individuals with a tendency to move in circles appear at rare intervals in
races of common mice. It seems highly probable, in view of these facts,
that the Chinese took advantage of a deviation from the usual form of
behavior to develop by means of careful and patient selectional breeding a
race of mice which is remarkable for its dancing. Even if it should be
proved that the mutation as it appears among common mice is not inherited,
the view that slight deviations were taken advantage of by the breeders
would still be tenable. The dancing tendency is such in nature as to unfit
an individual for the usual conditions of mouse existence, hence, in all
probability human care alone could have produced and preserved the race of
dancers.
In answer to the question, how and when did the race of dancers originate,
it may be said that historical research indicates that a structural
variation or mutation which occasionally appears in _Mus musculus_, and
causes those peculiarities of movement which are known as dancing, has
been preserved and accentuated through selectional breeding by the Chinese
and Japanese, until finally a distinct race of mice which breeds true to
the dance character has been established. The age of the race is not
definitely known, but it is supposed to have existed for several
centuries.
CHAPTER II
FEEDING, BREEDING, AND DEVELOPMENT OF THE YOUNG
In this chapter I shall report, for the benefit of those who may wish to
know how to take care of dancing mice, my experience in keeping and
breeding the animals, and my observations concerning the development of
the young. It is commonly stated that the dancer is extremely delicate,
subject to diseases to an unusual degree and difficult to breed. I have
not found this to be true. At first I failed to get them to breed, but
this was due, as I discovered later, to the lack of proper food. For three
years my mice have bred frequently and reared almost all of their young.
During one year, after I had learned how to care for the animals, when the
maximum number under observation at any time was fifty and the total
number for the year about one hundred, I lost two by disease and one by an
accident. I very much doubt whether I could have done better with any
species of mouse. There can be no doubt, however, that the dancer is
delicate and demands more careful attention than do most mice. In March,
1907, I lost almost all of my dancers from what appeared to be an
intestinal trouble, but with this exception I have had remarkably good
luck in breeding and rearing them.
My dancers usually were kept in the type of cage of which Figure 2 is a
photograph.[1] Four of these double cages, 70 cm. long, 45 cm. wide, and
10 cm. deep in front, were supported by a frame as is shown in Figure 3.
The fact that the covers of these cages cannot be left open is of
practical importance. A similar type of cage, which I have used to some
extent, consists of a wooden box 30 by 30 cm. by 15 cm. deep, without any
bottom, and with a hinged cover made in part of 1 cm. mesh wire netting.
Such a cage may be placed upon a piece of tin or board, or simply on a
newspaper spread out on a table. The advantage of the loose bottom is that
the box may be lifted off at any time, and the bottom thoroughly cleansed.
I have had this type of cage constructed in blocks of four so that a
single bottom and cover sufficed for the block. If the mice are being kept
for show or for the observation of their movements, at least one side of
the cages should be of wire netting, and, as Kishi suggests, such objects
as a wheel, a tower, a tunnel, a bridge, and a turntable, if placed in the
cage, will give the animals excellent opportunity to exhibit their
capacity for varied forms of activity.
[Footnote 1: This cage was devised by Professors W.E. Castle and E.L.
Mark, and has been used in the Zoological Laboratories of Harvard
University for several years.]
[Illustration: FIGURE 2.--Double cage, with nest boxes and water dishes.]
The floors of the cages were covered with a thin layer of sawdust for the
sake of cleanliness, and in one corner of each cage a nest box of some
sort was placed. During the warm months I found it convenient and
satisfactory to use berry boxes, such as appear in Figure 2, with a small
entrance hole cut in one side; and during the cold months cigar boxes,
with an entrance hole not more than 5 cm. in diameter at one end. In the
nest box a quantity of tissue paper, torn into fragments, furnished
material for a nest in which the adults could make themselves comfortable
or the female care for her young. Cotton should never be used in the nest
boxes, for the mice are likely to get it wound about their legs with
serious results. Apparently they are quite unable to free themselves from
such an incumbrance, and their spinning motion soon winds the threads so
tightly that the circulation of the blood is stopped.
[Illustration: FIGURE 3.--Double cages in frame.]
The cages and nest boxes were emptied and thoroughly cleaned once a week
with an emulsion made by heating together one part of kerosene and one
part of water containing a little soap. This served to destroy whatever
odor the cages had acquired and to prevent vermin from infesting the
nests. In hot weather far greater cleanliness is necessary for the welfare
of the mice than in cold weather. The animals attend faithfully to their
own toilets, and usually keep themselves scrupulously clean.
For water and food dishes I have used heavy watch glasses[1] 5 cm. in
diameter and 1/2 cm. deep. They are convenient because they are durable,
easily cleaned, and not large enough for the young mice to drown in when
they happen to spin into one which contains water. It is said that mice do
not need water, but as the dancers seem very fond of a little, I have made
it a rule to wash the watch glasses thoroughly and fill them with pure
fresh water daily. The food, when moist, may be placed in the cages in the
same kind of watch glass.
[Footnote 1: Minot watch glasses.]
There is no need of feeding the animals oftener than once a day, and as
they eat mostly in the evening and during the night, it is desirable that
the food should be placed in the cage late in the afternoon. For almost a
year I kept a pair of dancers on "force"[1] and water. They seemed
perfectly healthy and were active during the whole time, but they produced
no young. If the animals are kept as pets, and breeding is not desired, a
diet of "force," "egg-o-see,"[1] and crackers, with some bird-seed every
few days, is likely to prove satisfactory. As with other animals, a
variety of food is beneficial, but it appears to be quite unnecessary. Too
much rich food should not be given, and the mice should be permitted to
dictate their own diet by revealing their preferences. They eat
surprisingly little for the amount of their activity. I have had excellent
success in breeding the mice by feeding them a mixture of dry bread-
crumbs, "force," and sweet, clean oats slightly moistened with milk. The
food should never be made soppy. A little milk added thus to the food
every other day greatly increases fertility. About once a week a small
quantity of some green food, lettuce for example, should be given. It is
well, I have found, to vary the diet by replacing the bread and "force" at
intervals with crackers and seeds. Usually I give the food dry every other
day, except in the case of mice which are nursing litters. One person to
whom I suggested that lettuce was good for the dancers lost four,
apparently because of too much of what the mice seemed to consider a good
thing. This suggests that it should be used sparingly.
[Footnote 1: A cereal food.]
Success in keeping and breeding dancing mice depends upon three things:
cleanliness, warmth, and food supply. The temperature should be fairly
constant, between 60° and 70° Fahr. They cannot stand exposure to cold or
lack of food. If one obtains good healthy, fertile individuals, keeps them
in perfectly clean cages with soft nesting materials, maintains a
temperature of not far above or below 65°, and regularly supplies them
with pure water and food which they like, there is not likely to be
trouble either in keeping or breeding these delicate little creatures.
Several persons who have reported to me difficulty in rearing the young or
in keeping the adults for long periods have been unable to maintain a
sufficiently high or constant temperature, or have given them food which
caused intestinal trouble.
The males are likely to fight if kept together, and they may even kill one
another. A male may be kept with one or more females, or several females
may be kept together, for the females rarely, in my experience, fight, and
the males seldom harm the females. Unless the male is removed from the
cage in which the female is kept before the young are born, he is likely
to kill the newborn animals. When a female is seen to be building a nest
in preparation for a litter, it is best to place her in a cage by herself
so that she may not be disturbed.
The sex of individuals may be determined easily in most cases, at the age
of 10 to 12 days, by the appearance of teats in the case of females.
The period of gestation is from 18 to 21 days. The maximum number born by
my dancers in any single litter was 9, the minimum number 3. In 25 litters
of which I have accurate records, 135 individuals were born, an average of
5.4. The average number of males per litter was precisely the same, 2.7,
as the number of females.
On the birth of a litter it is well to see that the female has made a nest
from which the young are not likely to escape, for at times, if the nest
is carelessly made, they get out of it or under some of the pieces of
paper which are used in its construction, and perish. Several times I have
observed nests so poorly built that almost all of the young perished
because they got too far away to find their way back to the mother. It is
surprising that the female should not take more pains to keep her young
safe by picking them up in her mouth, as does the common mouse, and
carrying them to a place where they can obtain warmth and nourishment.
This I have never seen a dancing mouse do. For the first day or two after
the birth of a litter the female usually remains in the nest box almost
constantly and eats little. About the second day she begins to eat
ravenously, and for the next three or four weeks she consumes at least
twice as much food as ordinarily. Alexander and Kreidl (3 p. 567) state
that the female does not dance during the first two weeks after the birth
of a litter, but my experience contradicts their statement. There is a
decreased amount of activity during this period, and usually the whirling
movement appears but rarely; but in some cases I have seen vigorous and
long-continued dancing within a few hours after the birth of a litter.
There is a wide range of variability in this matter, and the only safe
statement, in the light of my observations, is that the mother dances less
than usual for a few days after a litter is born to her.
The development of the young, as I have observed it in the cases of twenty
litters, for ten of which (Table I) systematic daily records were kept,
may be sketched as follows. At birth the mice have a rosy pink skin which
is devoid of hair and perfectly smooth; they are blind, deaf, and
irresponsive to stimulation of the vibrissae on the nose. During the first
week of post-natal life the members of a litter remain closely huddled
together in the nest, and no dance movements are exhibited. The mother
stays with them most of the time. On the fourth or fifth day colorless
hairs are visible, and by the end of the week the body is covered with a
coat which rapidly assumes the characteristic black and white markings of
the race. For the first few days the hind legs are too weak to support the
body weight, and whatever movements appear are the result of the use of
the fore legs. As soon as the young mice are able to stand, circling
movements are exhibited, and by the end of the second week they are
pronounced. Somewhere about the tenth day the appearance of the teats in
the case of the females serves to distinguish the sexes plainly. Between
the tenth and fifteenth days excitability, as indicated by restless jerky
movements in the presence of a disturbing condition, increases markedly;
the auditory meatus opens, and, in the case of some individuals, there are
signs of hearing. On or after the fifteenth day the eyes open and the
efforts to escape from the nest box rapidly become more vigorous. About
this time the mother resumes her dancing with customary vigor, and the
young, when they have opportunity, begin to eat of the food which is given
to her. They now dance essentially as do the adults. From the end of the
third week growth continues without noteworthy external changes until
sexual maturity is attained, between the fourth and the sixth week. For
several weeks after they are sexually mature the mice continue to increase
in size.
TABLE I
DEVELOPMENT OF THE YOUNG
NUMBER JERKY REACT
IN HAIR TEATS MOVE- EARS TO EYES
PARENTS LITTER VISIBLE VISIBLE MENTS OPEN SOUND OPEN
M F APPEAR
152+151 5 0 4th day -- 13th day 14th day 14th day 16th day
152+151 1 3 4th day 9th day 10th day 12th day 13th day 15th day
410+415 4 1 5th day 11th day 14th day 15th day 15th day 17th day
410+415 2 4 5th day 10th day 13th day 14th day 14th day 16th day
420+425 0 2 4th day 10th day 12th day 14th day 14th day 16th day
210+215 4 1 -- -- 17th day 13th day 17th day 15th day
210+215 3 3 5th day 11th day 11th day 14th day No 16th day
212+211 1 3 4th day 10th day 15th day 14th day No 15th day
220+225 2 4 4th day 10th day 16th day 14th day No 15th day
220+225 3 3 4th day 10th day 17th day 13th day No 15th day
A course of development very similar to that just described was observed
by Alexander and Kreidl (3 p. 565) in three litters of dancing mice which
contained 3, 5, and 7 individuals respectively. These authors, in
comparing the development of the dancer with that of the common mouse, say
that at birth the young in both cases are about 24 mm. in length. The
young common mouse grows much more rapidly than the dancer, and by the
ninth day its length is about 43 mm. as compared with 31 mm. in the case
of the dancer. According to Zoth (31 p. 148) the adult dancer has a body
length of from 7 to 7.5 cm., a length from tip of nose to tip of tail of
from 12 to 13 cm., and a weight of about 18 grams. The movement of the
dancer from the first tends to take the form of circles toward the middle
of the nest; that of the common mouse has no definite tendency as to
direction. When the common mouse does move in circles, it goes first in
one direction, then in the other, and not for any considerable period in
one direction as does the true dancer. Neither the young dancer nor the
common mouse is able to equilibrate itself well for the first few days
after birth, but the latter can follow a narrow path with far greater
accuracy and steadiness than the former. The uncertain and irregular
movements of the common mouse are due to muscular weakness and to
blindness, but the bizarre movements of the young dancer seem to demand
some additional facts as an explanation.
A brief account of the development of the dancer given by Zoth (31 p. 149)
adds nothing of importance to the description given by Alexander and
Kreidl. As my own observations disagree with their accounts in certain
respects, I shall now give, in the form of a diary, a description of the
important changes observed from day to day in a normal litter. The litter
which I have selected as typical of the course of development in the
dancer grew rapidly under favorable conditions. I have observed many
litters which passed through the various stages of development mentioned
in this description anywhere from a day to a week later. This was usually
due to some such obviously unfavorable condition as too little food or
slight digestive or bowel troubles. According to the nature of the
conditions of growth the eyes of the dancer open anywhere from the
fourteenth to the twentieth day. This statement may serve to indicate the
degree of variability as to the time at which a given stage of development
is reached by different litters.
On July 14, 1906, No. 151 (female) and No. 152 (male) were mated, and on
August 3 a litter of six was born to them. The course of the development
of this litter during the first three weeks was as follows:--
_First day_ The skin is pink and hairless, several vibrissae are visible
on the nose and lips, but there is no definite response when they are
touched. The mice are both blind and deaf, but they are able to squeak
vigorously. The mother was not seen to dance or eat during the day.
_Second day_. There is a very noticeable increase in size. The vibrissae
are longer, but touching them still fails to cause a reaction. No hairs
are visible on the body. The mother danced rapidly for periods of a minute
several times while the record was being made. She ate very little to-day.
_Third day_. Scales began to appear on the skin to-day. The animals are
rapidly increasing in strength; they can now crawl about the nest easily,
but they are too weak to stand, and constantly roll over upon their sides
or backs when they are placed on a smooth surface. Because of their
inability to progress it is impossible to determine with certainty whether
they have a tendency to move in circles. The mother was seen out of the
nest dancing once to-day. She now eats ravenously.
_Fourth day_. One of the six young mice was found under a corner of the
nest this morning dead, and the others were scattered about the nest box.
I gathered them together into a nest which I made out of bits of tissue
paper, and the mother immediately began to suckle them. They are very
sensitive to currents of air, but they do not respond to light or sound
and seldom to contact with the vibrissae.
_Fifth day_. When placed on a smooth surface, they tend to move in
circles, frequently rolling over. When placed on their sides or backs,
they immediately try to right themselves. They do not walk, for their legs
are still too weak to support the weight of the body; instead they drag
themselves about by the use of the fore legs. Fine colorless hairs are
visible over the entire body surface. When the vibrissae are touched, the
head is moved noticeably. The mother dances a great deal and eats about
twice as much as she did before the birth of the litter.
_Sixth day_. Certain regions of the skin, which were slightly darker than
the remainder on the fourth and fifth days, are now almost black. It is
evident that they are the regions in which the black hair is to appear.
The movement in circles is much more definite today, although most of the
individuals are still too weak to stand on their feet steadily for more
than a few seconds at a time. Most of their time, when they are first
taken from the nest, is spent in trying to maintain or regain an upright
position. The hair is now easily visible, and the skin begins to have a
white appearance as a result.
_Seventh day_. Although they are strong enough to move about the nest
readily, none of the young has attempted to leave the nest. They huddle
together in the middle of it for warmth. The epidermal scales, which have
increased in number since the third day, are dropping off rapidly. Contact
with the vibrissae or with the surface of the body, frequently calls forth
a motor reaction but neither light nor sound produces any visible change
in behavior. The black and white regions of the skin are sufficiently
definite now to enable one to distinguish the various individuals by their
markings. The mother was seen to dance repeatedly today, and she ate all
the food that was given to her.
_Eighth day_. A fold is plainly visible where later the eyelids will
separate. The black pigment in the skin has increased markedly.
_Ninth day_. The eyelids are taking form rapidly, but they I have not
separated. The body is covered with a thick coat of hair which is either
pure white or black. Standing on the four legs is still a difficult task.
_Tenth day_. To-day teats are plainly visible in the case of four of the
five individuals of the litter. Up to this time I had thought, from
structural indications, that there were three males and two females; it is
now evident that there are four females and one male. The external ear,
the pinna, is well formed, and has begun to stand out from the head, but
no opening to the inner portion of the ear is present. The eyelids appear
to be almost fully formed.
_Eleventh day_. There are no very noticeable changes in appearance except
in size, which continues to increase rapidly. They are able to regain
their normal upright position almost immediately when they happen to roll
over. The mother dances as usual.
_Twelfth day_. It appears to-day as if the eyes were about to open. The
ears are still closed, and there is no evidence of a sense of hearing.
They squeaked considerably when in the nest, but not at all when I took
them out to note their development. The mother stays outside of the nest
box much of the time now, probably to prevent the young ones from sucking
continuously.
_Thirteenth day_. One of the little mice came out of the nest box while I
was watching the litter this morning, and was able to find his way back
directly despite the lack of sight. The mice are still dependent upon the
mother for nourishment. I have not seen any of them attempt to eat the
food which is given to the mother. They are extremely neat and clean. I
watched one of them wash himself this morning. Each foot was carefully
licked with the tongue. There seems to be special care taken to keep the
toes perfectly clean.
_Fourteenth day_. An opening into the ear is visible to-day. When tested
with the Galton whistle, all five responded with quick, jerky movements of
the head and legs. They evidently hear certain tones. During the past two
days the ears have changed rapidly. In one of the females, which seems to
be a little in advance of the others in development, certain peculiarities
of behavior appeared to-day. She jumped and squeaked sharply when touched
and sprang out of my hand when I attempted to take her up. This is in
marked contrast with her behavior previously.
_Fifteenth day_. The eyes are partly opened. All of the members of the
litter came out of the nest box this morning and ran around the cage,
dancing frequently and trying to eat with the mother. Three out of the
five gave auditory reactions on first being stimulated; none of them
responded to repetitions of the stimulus. All appeared to be less
sensitive to sounds than yesterday. The quick, nervous, jerky movements
are very noticeable.
_Sixteenth day_. The eyes of all five are fully opened. They dance
vigorously and are outside the nest much of the time.
_Seventeenth day_. No reactions to sound could be detected to-day. The
sense of sight gives evidence of being well developed. The nervous jumping
movements persist.
_Eighteenth day_. The young mice continue to suck, although they eat of
the food which is given to the mother. They are now able to take care of
themselves.
_Nineteenth day_. There are no noteworthy changes except increase in size
and strength.
_Twentieth day_. No auditory reactions were obtained today, but other
forms of stimulation brought about unmistakable responses.
_Twenty-first day_. They are now about half grown and there is no other
change of special interest to be recorded. Growth continues for several
weeks. The statement made by Alexander and Kreidl to the effect that the
dancer is almost full grown by the thirty-first day of life is false. At
that age they may be sexually mature, but usually they are far from full
grown.
CHAPTER III
BEHAVIOR: DANCE MOVEMENTS
The peculiarities of behavior of the dancing mouse are responsible alike
for the widespread interest which it has aroused, and for its name. In a
little book on fancy varieties of mice, in which there is much valuable
information concerning the care of the animals, one who styles himself "An
old fancier" writes thus of the behavior of the dancer: "I believe most
people have an idea that the waltzing is a stately dance executed on the
hind feet; this is not so. The performer simply goes round and round on
all fours, as fast as possible, the head pointing inwards. The giddy
whirl, after continuing for about a dozen turns, is then reversed in
direction, and each performance usually occupies from one to two minutes.
Whether it is voluntary or not, is difficult to determine, but I am
inclined to think the mouse can refrain if it wishes to do so, because I
never see them drop any food they may be eating, and begin to waltz in the
midst of their meal. The dance, if such it can be called, generally seizes
the mouse when it first emerges from its darkened sleeping place, and this
would lead one to suppose that the light conveys an impression of shock to
the brain, through the eyes, which disturbs the diseased centers and
starts the giddy gyrations. The mice can walk or run in a fairly straight
line when they wish to do so." Some of the old fancier's statements are
true, others are mere guesses. Those who have studied the mice carefully
will doubtless agree that he has not adequately described the various
forms of behavior of which they are capable. I have quoted his description
as an illustration of the weakness which is characteristic of most popular
accounts of animal behavior. It proves that it is not sufficient to watch
and then describe. The fact is that he who adequately describes the
behavior of any animal watches again and again under natural and
experimental conditions, and by prolonged and patient observation makes
himself so familiar with his subject that it comes to possess an
individuality as distinctive as that of his human companions. To the
casual observer the individuals of a strange race are almost
indistinguishable. Similarly, the behavior of all the animals of a
particular species seems the same to all except the observer who has
devoted himself whole-heartedly to the study of the subject and who has
thus become as familiar with their life of action as most of us are with
that of our fellow-men; for him each individual has its own unmistakable
characteristics.
I shall now describe the behavior of the dancing mouse in the light of the
results of the observation of scores of individuals for months at a time,
and of a large number of experiments. From time to time I shall refer to
points in the accounts of the subject previously given by Rawitz (25 p.
236), Cyon (9 p. 214), Alexander and Kreidl (1 p. 542), Zoth (31 p. 147),
and Kishi (21 p. 479).
The most striking features of the ordinary behavior of the dancer are
restlessness and movements in circles. The true dancer seldom runs in a
straight line for more than a few centimeters, although, contrary to the
statements of Rawitz and Cyon, it is able to do so on occasion for longer
distances. Even before it is old enough to escape from the nest it begins
to move in circles and to exhibit the quick, jerky head movements which
are characteristic of the race. At the age of three weeks it is able to
dance vigorously, and is incessantly active when not washing itself,
eating, or sleeping. According to Zoth (31 p. 149) the sense of sight and
especially the sense of smell of the dancer "seem to be keenly developed;
one can seldom remain for some time near the cage without one or another
of the animals growing lively, looking out of the nest, and beginning to
sniff around in the air (_windet_). They also seem to have strongly
developed cutaneous sensitiveness, and a considerable amount of curiosity,
if one may call it such, in common with their cousin, the white mouse." I
shall reserve what I have to say concerning the sense of sight for later
chapters. As for the sense of smell and the cutaneous sensitiveness, Zoth
is undoubtedly right in inferring from the behavior of the animal that it
is sensitive to certain odors and to changes in temperature. One of the
most noticeable and characteristic activities of the dancer is its
sniffing. Frequently in the midst of its dancing it stops suddenly, raises
its head so that the nose is pointed upward, as in the case of one of the
mice of the frontispiece, and remains in that position for a second or
two, as if sniffing the air.
The restlessness, the varied and almost incessant movements, and the
peculiar excitability of the dancer have repeatedly suggested to casual
observers the question, why does it move about in that aimless, useless
fashion? To this query Rawitz has replied that the lack of certain senses
compels the animal to strive through varied movements to use to the
greatest advantage those senses which it does possess. In Rawitz's opinion
the lack of hearing and orientation is compensated for by the continuous
use of sight and smell. The mouse runs about rapidly, moves its head from
side to side, and sniffs the air, in order that it may see and smell as
much as possible. In support of this interpretation of the restlessness of
the dancer, Rawitz states that he once observed similar behavior in an
albino dog which was deaf. This suggestion is not absurd, for it seems
quite probable that the dancer has to depend for the guidance of its
movements upon sense data which are relatively unimportant in the common
mouse, and that by its varied and restless movements it does in part make
up for its deficiency in sense equipment.
The dancing, waltzing, or circus course movement, as it is variously
known, varies in form from moment to moment. Now an individual moves its
head rapidly from side to side, perhaps backing a little at the same time,
now it spins around like a top with such speed that head and tail are
almost indistinguishable, now it runs in circles of from 5 cm. to 30 cm.
in diameter. If there are any objects in the cage about or through which
it may run, they are sure to direct the expression of activity. A tunnel
or a hole in a box calls forth endless repetitions of the act of passing
through. When two individuals are in the same cage, they frequently dance
together, sometimes moving in the same direction, sometimes in opposite
directions. Often, as one spins rapidly about a vertical axis, the other
runs around the first in small circles; or again, both may run in a small
circle in the same direction, so that their bodies form a living ring,
which, because of the rapidity of their movements, appears perfectly
continuous. The three most clearly distinguishable forms of dance are (1)
movement in circles with all the feet close together under the body, (2)
movement in circles, which vary in diameter from 5 cm. to 30 cm., with the
feet spread widely, and (3) movement now to the right, now to the left, in
figure eights ([Symbol: figure eight]). For convenience of reference
these types of dance may be called _whirling, circling_, and the _figure
eight dance_. Zoth, in an excellent account of the behavior of the dancer
(31 p. 156), describes "manège movements," "solo dances," and "centre
dances." Of these the first is whirling, the second one form of circling,
and the third the dancing of two individuals together in the manner
described above.
Both the whirling and the circling occur to the right (clockwise) and to
the left (anticlockwise). As certain observers have stated that it is
chiefly to the left and others that it is as frequently to the right, I
have attempted to get definite information concerning the matter by
observing a number of individuals systematically and at stated intervals.
My study of this subject soon convinced me that a true conception of the
facts cannot be got simply by noting the direction of turning from time to
time. I therefore planned and carried out a series of experimental
observations with twenty dancers, ten of each sex. One at a time these
individuals were placed in a glass jar, 26 cm. in diameter, and the number
of circle movements executed to the right and to the left during a period
of five minutes was determined as accurately as possible. This was
repeated at six hours of the day: 9 and 11 o'clock A.M., and 2, 4, 6, and
8 o'clock P.M. In order that habituation to the conditions under which the
counts of turning were made might hot influence the results for the group,
with ten individuals the morning counts were made first, and with the
others the afternoon counts. No attempt was made in the counting to keep a
separate record of the whirling and circling, although had it been
practicable this would have been desirable, for, as soon became evident to
the observer, some individuals which whirl in only one direction, circle
in both.
In Table 2 the results of the counts for the males are recorded; in Table
3 those for the females. Each number in the column headed "right" and
"left" indicates the total number of circles executed by a certain dancer
in a period of five minutes at the hour of the day named at the head of
the column. I may point out briefly the curiously interesting and entirely
unexpected new facts which this method of observation revealed to me.
First, there are three kinds of dancers: those which whirl almost
uniformly toward the right, those which whirl just as uniformly toward the
left, and those which whirl about as frequently in one direction as in the
other. To illustrate, No. 2 of Table 2 may be characterized as a "right
whirler," for he turned to the right almost uniformly. In the case of the
6 P.M. count, for example, he turned 285 times to the right, not once to
the left. No. 152, on the contrary, should be characterized as a "left
whirler," since he almost always turned to the left. From both of these
individuals No. 210 is distinguished by the fact that he turned now to the
left, now to the right. For him the name "mixed whirler" seems
appropriate.
Second, the amount of activity, as indicated by the number of times an
individual turns in a circle within five minutes, increases regularly and
rapidly from 9 A.M. to 8 P.M. According to the general averages which
appear at the bottom of Table 2, the average number of circles executed by
the males at 9 A.M. was 89.8 as compared with 207.1 at 8 P.M. In other
words, the mice dance more in the evening than during the day.
Third, as it appears in a comparison of the general averages of Tables 2
and 3, the females dance more than the males, under the conditions of
observation. At 9 A.M. the males circled 89.8 times, the females 151.0
times; at 8 P.M. the males circled 207.1 times, the females, 279.0 times.
Fourth, according to the averages for the six counts made with each
individual, as they appear in Table 4, the males turn somewhat more
frequently to the left than to the right (the difference, however, is not
sufficient to be considered significant); whereas, the females turn much
more frequently to the right than to the left. I do not wish to emphasize
the importance of this difference, for it is not improbable that counts
made with a larger number of animals, or even with another group of
twenty, would yield different results.
TABLE 2
NUMBER or WHIRLS TO THE RIGHT AND TO THE LEFT DURING
FIVE-MINUTE INTERVALS AS DETERMINED BY COUNTS MADE AT
SIX DIFFERENT HOURS, FOR EACH OF TEN MALE DANCERS
NUMBER 9 A.M 11 A.M. 2 P.M.
OF
ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT
2 11 2 23 4 194 1
30 20 1 134 1 109 2
34 2 16 2 48 4 92
36 194 21 180 11 143 65
152 7 48 3 171 6 79
156 63 8 53 9 27 6
210 3 9 7 41 225 21
220 168 105 39 43 47 5
410 2 67 10 27 8 103
420 15 142 5 214 16 238
Averages 48.5 41.3 45.6 56.9 77.9 61.2
Gen. Av. 89.8 102.5 139.1
NUMBER 4 P.M 6 P.M. 8 P.M.
OF
ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT
2 70 3 285 0 237 10
30 154 0 107 6 134 5
34 7 158 5 118 6 147
36 173 14 170 11 325 19
152 0 91 16 210 9 223
156 85 2 72 26 139 26
210 159 18 31 82 47 201
220 45 38 78 17 69 33
410 9 155 9 394 24 94
420 18 243 16 291 3 320
Averages 72.0 72.2 78.9 115.5 99.3 107.8
Gen. Av. 144.2 194.4 207.1
TABLE 3
NUMBER OF WHIRLS TO THE RIGHT AND TO THE LEFT DURING
FIVE-MINUTE INTERVALS AS DETERMINED BY COUNTS MADE AT
SIX DIFFERENT HOURS, FOR EACH OF TEN FEMALE DANCERS
NUMBER 9 A.M. 11 A.M. 2 P.M.
OF
ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT
29 9 18 17 30 7 22
33 287 0 329 1 352 3
35 48 15 198 46 208 14
151 13 88 7 75 3 167
157 57 6 50 45 53 12
211 218 21 31 55 66 5
215 67 216 33 105 37 226
225 46 39 72 49 143 44
415 23 0 156 0 34 3
425 43 296 12 201 12 210
Averages 81.1 69.9 90.5 60.7 91.5 70.6
Gen. Av. 151.0 151.2 162.1
NUMBER 4 P.M. 6 P.M. 8 P.M.
OF
ANIMAL RIGHT LEFT RIGHT LEFT RIGHT LEFT
29 33 114 31 36 45 99
33 436 7 408 3 364 2
35 279 6 165 24 353 10
151 3 8 2 285 2 217
157 52 15 19 125 51 104
211 190 7 86 31 67 250
215 15 292 45 336 150 232
225 133 86 48 39 177 81
415 268 3 437 7 382 8
425 12 242 19 210 4 192
Averages 142.1 78.0 126.0 109.6 159.5 119.5
Gen. Av. 220.1 235.6 279.0
The most important results of this statistical study of turning are the
demonstration of the existence of individual tendencies to turn in a
particular direction, and of the fact that the whirling increases in
amount from morning to evening.
In order to discover whether the distribution of the dancers among the
three groups which have been designated as right, left, and mixed whirlers
agrees in general with that indicated by Table 4 (approximately the same
number in each group) I have observed the direction of turning in the case
of one hundred dancers, including those of the foregoing tables, and have
classified them in accordance with their behavior as is indicated below.
RIGHT LEFT MIXED
WHIRLERS WHIRLERS WHIRLERS
Males 19 19 12
Females 12 23 15
Totals 31 42 27
The left whirlers occur in excess of both the right and the mixed
whirlers. This fact, together with the results which have already been
considered in connection with the counts of turning, suggests that a
tendency to whirl in a certain way may be inherited. I have examined my
data and conducted breeding experiments for the purpose of ascertaining
whether this is true. But as the results of this part of the investigation
more properly belong in a special chapter on the inheritance of behavior
(XVIII), the discussion of the subject may be closed for the present with
the statement that the preponderance of left whirlers indicated above is
due to a strong tendency to turn to the left which was exhibited by the
individuals of one line of descent.
TABLE 4
AVERAGE NUMBER OF WHIRLS TO THE RIGHT AND TO THE LEFT FOR
THE SIX INTERVALS OF TABLES 2 AND 3, WITH A CHARACTERIZATION
OF THE ANIMALS AS RIGHT WHIRLERS, LEFT WHIRLERS, OR
MIXED WHIRLERS.
AVERAGE NO. AVERAGE NO.
MALES AGE OF WHIRLS OF WHIRLS CHARACTERIZATION
2 12 mo. 136.7 3.3 Right whirler
30 2 mo. 109.7 2.5 Right whirler
34 2 mo. 4.3 96.5 Left whirler
36 2 mo. 197.5 23.5 Right whirler
152 6 mo. 6.8 137.0 Left whirler
156 1 mo. 73.2 12.8 Right whirler
210 3 mo. 78.7 62.0 Mixed whirler
220 4 mo. 74.3 40.2 Mixed whirler
410 3 mo. 10.3 139.0 Left whirler
420 3 mo. 12.2 241.3 Left whirler
Average 70.4 75.8 4 Right whirlers
4 Left whirlers
2 Mixed whirlers
FEMALES
29 2 mo. 23.7 53.2 Left whirler
33 2 mo. 362.7 2.7 Right whirler
35 2 mo. 208.5 19.2 Left whirler
151 6 mo. 5.0 140.0 Right whirler
157 1 mo. 47.0 51.2 Left whirler
211 3 mo. 109.7 61.5 Right whirler
215 3 mo. 57.8 234.5 Mixed whirler
225 4 mo. 103.2 56.3 Mixed whirler
415 3 mo. 216.7 3.5 Left whirler
425 3 mo. 17.0 225.2 Left whirler
Average 115.1 84.7 3 Right whirlers
4 Left whirlers
3 Mixed whirlers
The tendency of the dancer's activity to increase in amount toward
evening, which the results of Tables 2, 3, and 4 exhibit, demands further
consideration. Haacke (7 p. 337) and Kishi (21 p. 458) agree that the
dancing is most vigorous in the evening; but Alexander and Kreidl (i p.
544) assert, on the contrary, that the whirling of the individuals which
they observed bore no definite relation to the time of day and apparently
was not influenced in intensity thereby. Since the results of my own
observations contradict many of the statements made by the latter authors,
I suspect that they may not have watched their animals long enough to
discover the truth. The systematic records which I have kept indicate that
the mice remain quietly in their nests during the greater part of the day,
unless they are disturbed or come out to obtain food. Toward dusk they
emerge and dance with varying intensity for several hours. I have seldom
discovered one of them outside the nest between midnight and daylight. The
period of greatest activity is between 5 and 10 o'clock P.M.
Zoth states that he has observed the adult dancer whirl 79 times without
an instant's interruption, and I have counted as many as 110 whirls. It
seems rather absurd to say that an animal which can do this is weak.
Evidently the dancer is exceptionally strong in certain respects, although
it may be weak in others. Such general statements as are usually made fail
to do justice to the facts.
The supposition that light determines the periodicity of dancing is not
borne out by my observations, for I have found that the animals continue
to dance most vigorously toward evening, even when they are kept in a room
which is constantly illuminated. In all probability the periodicity of
activity is an expression of the habits of the mouse race rather than of
the immediate influence of any environmental condition. At some time in
the history of the dancer light probably did have an influence upon the
period of activity; but at present, as a result of the persistence of a
well-established racial tendency, the periodicity of dancing depends to a
greater extent upon internal than upon external conditions. During its
hours of quiescence it is possible to arouse the dancer and cause it to
whirl more or less vigorously by stimulating it strongly with intense
light, a weak electric current, or by placing two individuals which are
strangers to one another in the same cage; but the dancing thus induced is
seldom as rapid, varied, or as long-continued as that which is
characteristic of the evening hours.
One of the most interesting results of this study of the direction of
turning, from the observer's point of view, is the demonstration of the
fact that the truth concerning even so simple a matter as this can be
discovered only by long and careful observation. The casual observer of
the dancer gets an impression that it turns to the left more often than to
the right; he verifies his observation a few times and then asserts with
confidence that such is the truth about turning. That such a method of
getting knowledge of the behavior of the animal is worse than valueless is
clear in the light of the results of the systematic observations which
have just been reported. But, however important the progress which we may
have made by means of systematic observation of the phenomenon of turning,
it must not for one moment be supposed that the whole truth has been
discovered. Continued observation will undoubtedly reveal other important
facts concerning circling, whirling, and the periodicity of dancing, not
to mention the inheritance of peculiarities of dancing and the
significance of the various forms of activity.
CHAPTER IV
BEHAVIOR: EQUILIBRATION AND DIZZINESS
Quite as interesting and important as the general facts of behavior which
we have been considering are the results of experimental tests of the
dancer's ability to maintain its position under unusual spatial
conditions--to climb, cross narrow bridges, balance itself on high places.
Because of its tendency to circle and whirl, to dart hither and thither
rapidly and apparently without control of its movements, the study of the
mouse's ability to perform movements which demand accurate and delicate
muscular coördination, and to control its expressions of activity, are of
peculiar scientific interest.
That observers do not entirely agree as to the facts in this field is
apparent from the following comparison of the statements made by Cyon and
Zoth (31 p. 174).
Cyon states that the dancer
Cannot run in a straight line,
Cannot turn in a narrow space,
Cannot run backward,
Cannot run up an incline,
Cannot move about safely when above the ground, because of
fear and visual dizziness,
Can hear certain tones.
Zoth, on the contrary, maintains that the animal
Can run in a straight line for at least 20 cm.,
Can and repeatedly does turn in a narrow space,
Can run backward, for he has observed it do so,
Can run up an incline unless the surface is too smooth for it to
gain a foothold,
Can move about safely when above the ground, and gives no
signs of fear or dizziness,
Cannot hear, or at least gives no signs of sensitiveness to sounds.
Such contradictory statements (and unfortunately they are exceedingly
common) stimulated me to the repetition of many of the experiments which
have been made by other investigators to test the dancer's behavior in
unusual spatial relations. I shall state very briefly the general
conclusions to which these experiments have led me, with only sufficient
reference to methods and details of results to enable any one who wishes
to repeat the tests for himself to do so. For the sake of convenience of
presentation and clearness, the facts have been arranged under three
rubrics: equilibrational ability, dizziness, and behavior when blinded. To
our knowledge of each of these three groups of facts important
contributions have come from the experiments of Cyon (9 p. 220), Alexander
and Kreidl (1 p. 545), Zoth (31 p. 157), and Kishi (21 p. 482), although,
as has been stated, in many instances their results are so contradictory
as to demand reexamination. All in all, Zoth has given the most
satisfactory account of the behavior and motor capacity of the dancer.
If the surface upon which it is moving be sufficiently soft or rough to
furnish it a foothold, the dancer is able to run up or down inclines, even
though they be very steep, to cross narrow bridges, to balance itself at
heights of at least 30 cm. above the ground, and even to climb up and down
on rods, as is shown by certain of Zoth's photographs which are reproduced
in Figure 4. Zoth himself says, and in this I am able fully to agree with
him on the basis of my own observations, "that the power of equilibration
in the dancing mouse, is, in general, very complete. The seeming reduction
which appears under certain conditions should be attributed, not to visual
dizziness, but in part to excitability and restlessness, and in part to a
reduced muscular power" (31 p. 161). The dancer certainly has far less
grasping power than the common mouse, and is therefore at a disadvantage
in moving about on sloping surfaces. One evidence of this fact is the
character of the tracks made by the animal. Instead of raising its feet
from the substratum and placing them neatly, as does the common mouse
(Figure 5), it tends to shuffle along, dragging its toes and thus
producing on smoked paper such tracks as are seen in Figure 6. From my own
observations I am confident that these figures exaggerate the differences.
My dancers, unless they were greatly excited or moving under conditions of
stress, never dragged their toes as much as is indicated in Figure 6.
However, there can be no doubt that they possess less power of grasping
with their toes than do common mice. The animal is still further
incapacitated for movement on inclined surfaces or narrow places by its
tendency to move in circles and zigzags. The results of my own experiments
indicate that the timidity of the adult is greater than that of the
immature animal when it is placed on a bridge 1 or 2 cm. wide at a
distance of 20 cm. from the ground. Individuals three weeks old showed
less hesitation about trying to creep along such a narrow pathway than did
full-grown dancers three or four months old; and these, in turn, were not
so timid apparently as an individual one year old. But the younger animals
fell off more frequently than did the older ones.
[Illustration: FIGURE 4.--Zoth's photographs of dancers crossing bridges
and climbing rods. Reproduced from _Pfluger's Archiv_, Bd. 86.]
[Illustration: FIGURE 5--Tracks of common mouse Reproduced from Alexander
and Kreidl's figure in _Pfluger's Archiv_, Bd 82]
[Illustration: FIGURE 6--Tracks of dancing mouse Reproduced from Alexander
and Kreidl's figure in _Pfluger's Archiv_ Bd 82]
Additional support for these statements concerning equilibrational ability
is furnished by the observations of Kishi (21 p. 482). He built a wooden
bridge 60 cm. long, 1 cm. wide at one end, and 1/2 cm. at the other, and
supported it at a height of 30 cm. above the ground by posts at the ends.
On this bridge ten dancers were tested. Some attempted to move sidewise,
others began to whirl and fell to the ground; only one of the ten
succeeded in getting all the way across the bridge on the first trial. The
second time he was tested this individual crossed the bridge and found the
post; and the third time he crossed the bridge and climbed down the post
directly. The others did not succeed in descending the post even after
having crossed the bridge safely, but, instead, finally fell to the floor
from awkwardness or exhaustion. On the basis of these and other similar
observations, Kishi says that the dancer possesses a fair degree of
ability to orient and balance itself.
Inasmuch as equilibration occurs similarly in darkness and in daylight,
Zoth thinks that there is neither visual dizziness nor fear of heights.
But it is doubtful whether he is right concerning fear. There is no doubt
in my mind, in view of the way the mice behave when placed on an elevated
surface, that they are timid; but this is due probably to the
uncomfortable and unusual position rather than to perception of their
distance from the ground. That they lack visual dizziness seems fairly
well established.
When rotated in a cyclostat[1] the dancer, unlike the common mouse, does
not exhibit symptoms of dizziness. The following vivid description of the
behavior of both kinds of mice when rotated is given by Alexander and
Kreidl (1 p. 548). I have not verified their observations.
[Footnote 1: An apparatus consisting of a glass cylinder with a mechanism
for turning it steadily and at different speeds about its vertical axis.]
The common mouse at first runs with increasing rapidity, as the speed of
rotation of the cyclostat cylinder is increased, in the direction opposite
to that of the cylinder itself. This continues until the speed of rotation
has increased to about 60 revolutions per minute. As the rotation becomes
still more rapid the mouse begins to crawl along the floor, its body
stretched out and clinging to the floor. At a speed of 250 revolutions per
minute it lies flat on the floor with its limbs extended obliquely to the
movement of rotation, and at times with its back bent against the axis of
the cylinder; in this position it makes but few and feeble efforts to
crawl forward. When the rotation is suddenly stopped, the animal pulls
itself together, remains for some seconds with extended limbs lying on the
floor, and then suddenly falls into convulsions and trembles violently.
After several attacks of this kind, cramps appear and, despite its
resistance, the animal is thrown about, even into the air at times, as if
by an external force. This picture of the position assumed during rapid
rotation, and of cramps after the cessation of rotation (the typical
picture of rotation dizziness), is repeated with great uniformity in the
case of the common mouse. Within fifteen minutes after being returned to
its cage the animal recovers from the effects of its experience. This
description of the symptoms of rotation dizziness in the common mouse
applies equally well to the blinded and the seeing animal.
In sharp contrast with the behavior of the common mouse in the cyclostat
is that of the dancer. As the cylinder begins to rotate the dancer runs
about as usual in circles, zigzags, and figure-eights. As the speed
becomes greater it naturally becomes increasingly difficult for the mouse
to do this, but it shows neither discomfort nor fear, as does the common
mouse. Finally the centrifugal force becomes so great that the animal is
thrown against the wall of the cylinder, where it remains quietly without
taking the oblique position. When the cyclostat is stopped suddenly, it
resumes its dance movements as if nothing unusual had occurred. It
exhibits no signs of dizziness, and apparently lacks the exhaustion which
is manifest in the case of other kinds of mice after several repetitions
of the experiment. The behavior of the blinded dancer is very similar.
If these statements are true, there is no reason to believe that the
dancer is capable of turning or rotation dizziness. If it were, its daily
life would be rendered very uncomfortable thereby, for its whirling would
constantly bring about the condition of dizziness. Apparently, then, the
dancer differs radically from most mammals in that it lacks visual and
rotational dizziness. In the next chapter we shall have to seek for the
structural causes for these facts.
The behavior of the blinded animal is so important in its bearings upon
the facts of orientation and equilibration that it must be considered in
connection with them. Cyon insists that the sense of vision is of great
importance to the dancer in orienting and equilibrating itself. When the
eyes are covered with cotton wads fastened by collodion, this writer
states (9 p. 223) that the mice behave as do pigeons and frogs whose
semicircular canals have been destroyed. They perform violent forced
movements, turn somersaults forward and backward, run up inclines and fall
over the edges, and roll over and over. In a word, they show precisely the
kind of disturbances of behavior which are characteristic of animals whose
semicircular canals are not functioning normally. Cyon, however, observed
that in certain dancers these peculiarities of behavior did not appear
when they were blinded, but that, instead, the animals gave no other
indication of being inconvenienced by the lack of sight than do common
white mice. This matter of individual differences we shall have to
consider more fully later.
No other observer agrees with Cyon in his conclusions concerning vision,
or, for that matter, in his statements concerning the behavior of the
blind dancer. Alexander and Kreidl (1 p. 550) contrast in the following
respects the behavior of the white mouse and that of the dancer when they
are blinded. The white mouse runs less securely and avoids obstacles less
certainly when deprived of vision. The dancer is much disturbed at first
by the shock caused by the removal of its eyes, or in case they are
covered, by the presence of the unusual obstruction. It soon recovers
sufficiently to become active, but it staggers, swerves often from side to
side, and frequently falls over. It moves clumsily and more slowly than
usual. Later these early indications of blindness may wholly disappear,
and only a slightly impaired ability to avoid obstacles remains.
It was noted by Kishi (21 p. 484), that the dancer when first blinded
trembles violently, jumps about wildly, and rolls over repeatedly, as Cyon
has stated; but Kishi believes that these disturbances of behavior are
temporary effects of the strong stimulation of certain reflex centers in
the nervous system. After having been blinded for only a few minutes the
dancers observed by him became fairly normal in their behavior. They moved
about somewhat more slowly than usually, especially when in a position
which required accurately coordinated movements. He therefore fully agrees
with Alexander and Kreidl in their conclusion that vision is not so
important for the guidance of the movements of the dancer as Cyon
believes.
In summing up the results of his investigation of this subject Zoth well
says (31 p. 168), "the orientation of the positions of the body with
respect to the horizontal and vertical planes seems to take place without
the assistance of the sense of sight." And, as I have already stated, this
excellent observer insists that the ability of the dancer to place its
body in a particular position (orientation), and its ability to maintain
its normal relations to its surroundings (equilibration) are excellent in
darkness and in daylight, provided only the substratum be not too smooth
for it to gain a foothold.
It must be admitted that the contradictions which exist in the several
accounts of the behavior of the dancer are too numerous and too serious to
be explained on the basis of careless observation. Only the assumption of
striking individual differences among dancers or of the existence of two
or more varieties of the animal suffices to account for the discrepancies.
That there are individual or variety differences is rendered practically
certain by the fact that Cyon himself worked with two groups of dancers
whose peculiarities he has described in detail, both as to structure and
behavior.
In the case of the first group, which consisted of three individuals, the
snout was more rounded than in the four individuals of the second group,
and there were present on the head three large tufts of bristly black hair
which gave the mice a very comical appearance. The animals of the second
group resembled more closely in appearance the common albino mouse. They
possessed the same pointed snout and long body, and only the presence of
black spots on the head and hips rendered them visibly different from the
albino mouse.
In behavior the individuals of these two groups differed strikingly. Those
of the first group danced frequently, violently, and in a variety of ways;
they seldom climbed on a vertical surface and when forced to move on an
incline they usually descended by sliding down backwards or sidewise
instead of turning around and coming down head first; they gave no signs
whatever of hearing sounds. Those of the second group, on the contrary,
danced very moderately and in few ways; they climbed the vertical walls of
their cage readily and willingly, and when descending from a height they
usually turned around and came down head first; two of the four evidently
heard certain sounds very well. No wonder that Cyon suggests the
possibility of a different origin! It seems not improbable that the
individuals of the second group were of mixed blood, possibly the result
of crosses with common mice.
As I shall hope to make clear in a subsequent discussion of the dancer's
peculiarities of behavior, in a chapter on individual differences, there
is no sufficient reason for doubting the general truth of Cyon's
description, although there is abundant evidence of his inaccuracy in
details. If, for the present, we accept without further evidence the
statement that there is more than one variety of dancer, we shall be able
to account for many of the apparent inaccuracies of description which are
to be found in the literature on the animal.
As a result of the examination of the facts which this chapter presents we
have discovered at least six important peculiarities of behavior of the
dancer which demand an explanation in terms of structure. These are: (1)
the dance movements--whirling, circling, figure-eights, zigzags; (2)
restlessness and the quick, jerky movements of the head; (3) lack of
responsiveness to sounds; (4) more or less pronounced deficiency in
orientational and equilibrational power; (5) lack of visual dizziness; (6)
lack of rotational dizziness.
Naturally enough, biologists from the first appearance of the dancing
mouse in Europe have been deeply interested in what we usually speak of as
the causes of these peculiarities of behavior. As a result, the structure
of those portions of the body which are supposed to have to do with the
control of movement, with the phenomena of dizziness, and with the ability
to respond to sounds, have been studied thoroughly. In the next chapter we
shall examine such facts of structure as have been discovered and attempt
to correlate them with the facts of behavior.
CHAPTER V
STRUCTURAL PECULIARITIES AND BEHAVIOR
The activities of an animal are expressions of changes which occur in its
structure, and they can be explained satisfactorily only when the facts of
structure are known. Such peculiarities of activity as are exhibited by
the dancing mouse, as contrasted with the common mouse, suggest at once
that this creature has a body which differs in important respects from
that of the ordinary mouse. In this chapter I shall present what is known
concerning the structural bases for the whirling, the lack of
equilibrational ability and of dizziness, the quick jerky head movements,
the restlessness, and the partial or total deafness of the dancing mouse.
Comparative physiologists have discovered that the ability of animals to
regulate the position of the body with respect to external objects and to
respond to sounds is dependent in large measure upon the groups of sense
organs which collectively are called the ear. Hence, with reason,
investigators who sought structural facts with which to explain the forms
of behavior characteristic of the dancer turned their attention first of
all to the study of the ear. But the ear of the animal is not, as might be
supposed on superficial examination, a perfectly satisfactory natural
experiment on the functions of this group of sensory structures, for it is
extremely uncertain whether any one of the usual functions of the organ is
totally lacking. Dizziness may be lacking, and in the adult hearing also,
but in general the functional facts lead the investigator to expect
modifications of the sense organs rather than their absence.
I shall now give an account of the results of studies concerning the
structure of the ear and brain of the dancer. Since the descriptions given
by different anatomists contradict one another in many important points,
the several investigations which have been made may best be considered
chronologically.
Bernhard Rawitz (25 p. 239) was the first investigator to describe the
structure of the ear of the Japanese or Chinese dancers, as he calls them.
The definite problem which he proposed to himself at the beginning of his
study was, what is the structural basis of the whirling movement and of
the deafness of the mice?
In his first paper Rawitz described the form of the ears of five dancers.
His method of work was to make microscopic preparations of the ears, and
from the sections, by the use of the Born method, to reconstruct the ear
in wax. These wax models were then drawn for the illustration of the
author's papers (Figures 8, 9, 10).
The principal results of the early work of Rawitz are summed up in the
following quotation from his paper: "The Japanese dancing mice have only
one normal canal and that is the anterior vertical. The horizontal and
posterior vertical canals are crippled, and frequently they are grown
together. The utriculus is a warped, irregular bag, whose sections have
become unrecognizable. The utriculus and sacculus are in wide-open
communication with each other and have almost become one. The utriculus
opens broadly into the scala tympani, and the nervous elements of the
cochlea are degenerate.
"The last-mentioned degeneration explains the deafness of the dancing
mice; but in my opinion it is a change of secondary nature. The primary
change is the broad opening between the utriculus and the scala tympani
from which results the streaming of the endolymph from the semicircular
canals into the cochlea. When, as a consequence of the rapid whirling
movements, a great part of the endolymph is hurled into the scala tympani,
the organ of Corti in the scala vestibuli is fixed and its parts are
rendered incapable of vibration. The condition of atrophy which is
observable in the sense cells and in the nerve elements is probably due to
the impossibility of functional activity; it is an atrophy caused by
disuse "(25 p. 242).
Ampulla externa
Ampulla anterior
Ramus utriculi
Membrana basilaris
Lagena
Canalis utriculo-saccularis
Membrana basilaris
Ampulla posterior
Macula acustica sacculi
[Illustration: FIGURE 7.--The inner ear of the rabbit. Reproduced from
Selenka after Retzius.]
To render the terms which occur in this and subsequent descriptions of the
ear of the dancer somewhat more intelligible to those who are not familiar
with the general anatomy of the vertebrate ear, a side view of the inner
ear of the rabbit is reproduced from a drawing by Retzius (Figure 7). I
have chosen the ear of the rabbit for this purpose, not in preference to
that of the common mouse, but simply because I failed to find any reliable
description of the latter with drawings which could be reproduced. The
rabbit's ear, however, is sufficiently like that of the mouse to make it
perfectly satisfactory for our present purpose.
This drawing of the rabbit's ear represents the three semicircular canals,
which occur in the ear of all mammals, and which are called, by reason of
their positions, the anterior vertical, the posterior vertical, and the
horizontal. Each of these membranous canals possesses at one end, in an
enlargement called the ampulla, a group of sense cells. In Figure 7 the
ampullae of the three canals are marked respectively, ampulla anterior,
ampulla posterior, and ampulla externa. This figure shows also the
cochlea, marked lagena, in which the organ of hearing of mammals (the
organ of Corti) is located. The ear sac, of which the chief divisions are
the utriculus and the sacculus, with which the canals communicate, is not
shown well in this drawing.
Within a few months after the publication of Rawitz's first paper on the
structure of the dancer's ear, another European investigator, Panse (23
and 24) published a short paper in which he claimed that previous to the
appearance of Rawitz's paper he had sectioned and mounted ears of the
common white mouse and the dancing mouse side by side, and, as the result
of careful comparison, found such slight differences in structure that he
considered them unworthy of mention. Panse, therefore, directly
contradicts the statements made by Rawitz. In fact, he goes so far as to
say that he found even greater differences between the ears of different
white mice than between them and the ears of the dancer (23 p. 140).
In a somewhat later paper Panse (24 p. 498) expresses his belief that,
since there are no peculiarities in the general form, sensory structures,
or nerve supply of the ear of the dancer, which serve to explain the
behavior of the animal, it is probable that there are unusual structural
conditions in the brain, perhaps in the cerebellum, to which are due the
dance movements and the deafness. The work of Panse is not very
convincing, however, for his figures are poor and his descriptions meager;
nevertheless, it casts a certain amount of doubt upon the reliability of
the descriptions given by Rawitz.
[Illustration: FIGURE 8.--The membranous labyrinth of the dancer's ear.
Type I. This figure, as well as 9 and 10, are reproduced from Rawitz's
figures in the _Archiv für Anatomie und Physiologie, Physiologische
Abtheilung_, 1899. _C.s._, anterior vertical canal; _C.p._, posterior
vertical canal; _C.e._, horizontal canal; _U._, utriculus.]
The unfavorable light in which his report was placed by Panse's statements
led Rawitz to examine additional preparations of the ear of the dancer.
Again he used the reconstruction method. The mice whose ears he studied
were sent to him by the physiologist Cyon.
As has been noted in Chapter IV, Cyon discovered certain differences in
the structure and in the behavior of these dancers (11 p. 431), which led
him to classify them in two groups. The individuals of one group climbed
readily on the vertical walls of their cages and responded vigorously to
sounds; those of the other group could not climb at all and gave no
evidences of hearing. After he had completed his study of their behavior,
Cyon killed the mice and sent their heads to Rawitz; but unfortunately
those of the two groups became mixed, and Rawitz was unable to distinguish
them. When he examined the structure of the ears of these mice, Rawitz did
find, according to his accounts, two structural types between which very
marked differences existed. Were it not for the carelessness which is
indicated by the confusion of the materials, and the influence of Cyon's
suggestion that there should be different structures to account for the
differences in behavior, Rawitz's statements might be accepted. As matters
stand there can be no doubt of individual differences in behavior,
external appearance, and the structure of the ear; but until these have
been correlated on the basis of thoroughgoing, careful observation, it is
scarcely worth while to discuss their relations.
[Illustration: FIGURE 9.--The membranous labyrinth of the dancer's ear.
Type II.]
[Illustration: FIGURE 10.--The membranous labyrinth of the dancer's ear.
Type III.]
To his previous description of the conditions of the ear sacs, sense
organs, and nerve elements of the dancer's ear, Rawitz adds nothing of
importance in his second paper (26 p. 171). He merely reiterates his
previous statements concerning the form of the canals, on the basis of his
findings in the case of six additional dancers. Figures 8, 9, and 10 are
reproduced from Rawitz to show the anatomical conditions which he claims
that he found. As these figures indicate, the canals were found to be
extremely variable, as well as unusual in form, and the sacs distorted. In
the ears of some specimens there were only two canals, and in all cases
they were more or less reduced in size, distorted, or grown together.
[Illustration: FIGURE 11.--Photograph of a wax model of the membranous
labyrinth of the ear of the dancer. Reproduced from Baginsky's figure in
the _Centralblatt für Physiologie_, Bd. 16.]
The work of Rawitz was unfavorably criticised by Alexander and Kreidl (2),
Kishi (21), and Baginsky (4), as well as by Panse (23 and 24). To their
criticisms Rawitz replied by insisting that the other investigators could
not with right attack his statements because they had not used the
reconstruction method. In order to test the value of this contention, and
if possible settle the question of fact, Baginsky had a model of the ear
of the dancer constructed by a skilled preparator (Herr Spitz) from
sections which had been prepared by the best neurological methods. This
model was made eighty times the size of the ear. It was then reduced in
the process of photographic reproduction to sixteen times the natural size
of the ear in the mouse. Figure 11 is a photograph of Baginsky's model. It
shows beyond question the presence of three canals of the same general
form and relations as those of the common mouse and of other mammals.
Baginsky's paper is brief and to the point. His criticisms of the work of
both Cyon and Rawitz are severe, but they are justified in all probability
by the carelessness of these investigators in the fixation of their
materials. Of the five skilled histologists who have examined the ear of
the dancer, Rawitz alone found markedly abnormal canals. It is highly
probable, therefore, that the canals in his preparations in some way
became distorted before the ears were sectioned. He doubtless described
accurately the conditions which he found, but the chances are that those
conditions never existed in the living animals.
The conflicting statements of Rawitz and Panse stimulated interest, and as
a result two other investigators, without knowledge of one another's work,
began careful researches on the dancer's ear. One, Alexander (2 and 3),
worked in coöperation with the physiologist Kreidl; the other, Kishi (21),
worked independently. The anatomical papers of Alexander and Kishi
appeared at about the same time, and since neither contains a reference to
the other, it is evident that the investigations were carried on almost
simultaneously. Alexander's descriptions are more detailed than those of
Rawitz and Panse, and in certain respects Kishi's are even more
thoroughgoing. The first paper published by Alexander and Kreidl (1)
contains the results of observations on the habits and behavior of the
dancers. Having examined the chief facts of function, these investigators
attempted to discover the structural conditions for the peculiarities of
behavior which they had observed.
As material for their anatomical work they made use of four dancers, one
albino mouse, and four common gray mice. The ears of these individuals
were fixed, sectioned, and examined microscopically in connection with
parts of the brain. In all, eight dancer ears and six common mouse ears
were studied.
Very extensive descriptions of these preparations, together with
measurements of many important portions of the ear, are presented in their
paper, the chief conclusions of which are the following:--
1. The semicircular canals, the ampullae, the utriculus, and the cristae
acusticae of the canals are normal in their general form and relations to
one another as well as in their histological conditions (2 p. 529). This
is contradictory of the statements made by Rawitz.
2. There is destruction of the macula sacculi (2 p. 534).
3. There is destruction also of the papilla basilaris cochleae, with
encroachment of the surrounding tissues in varying degrees.
4. There is diminution in the number of fibers of the branches and roots
of the ramus superior and ramus medius of the eighth nerve, and the fiber
bundles are very loosely bound together.
5. Similarly the number of fibers in the inferior branch (the cochlear
nerve) of the eighth nerve is very much reduced.
6. There is moderate reduction in the size of the two vestibular ganglia
as a result of the unusually small number of nerve cells.
7. The ganglion spirale is extremely degenerate.
There is therefore atrophy of the branches, ganglia, and roots of the
entire eighth nerve, together with atrophy and degeneration of the pars
inferior labyrinthii. The nerve endings are especially degenerate (2 p.
534).
The above structural deviations of the ear of the dancer from that of the
common mouse may be considered as primary or secondary according as they
are inherited or acquired. Since, according to Alexander and Kreidl, the
dancers' peculiarities of behavior and deafness are directly and uniformly
inherited, it is obvious that certain primary structural deviations must
serve as a basis for these functional facts. But it is equally clear, in
the opinion of Alexander and Kreidl (2 p. 536), that other structural
peculiarities of the dancer are the result of the primary changes, and in
no way the conditions for either the dancing or the deafness. These
authors feel confident that the facts of behavior which are to be
accounted for are almost certainly due to the pathological changes which
they have discovered in the nerves, ganglia, and especially in the
peripheral nerve endings of the ear of the mouse (2 p. 537).
It is further claimed by Alexander and Kreidl that there are very marked
individual differences among the dancers in the structure of the ear. In
some cases the otoliths and the sensory hairs are lacking; in others, they
are present in the state of development in which they are found in other
varieties of mouse. Sometimes the cochlea is much reduced in size; at
other times it is found to be of normal size (2 p. 538). These variations
in structure, if they really exist, go far toward justifying the tendency
of Cyon and Alexander and Kreidl, as well as many other investigators, to
regard the dancer as abnormal or even pathological.
The functions of the ear as at present known to the comparative
physiologist are grouped as the acoustic and the non-acoustic. The cochlea
is supposed on very good grounds to have to do with the acoustic
functions, and the organs of the semicircular canals on equally good
evidence are thought to have to do with such of the non-acoustic functions
as equilibration and orientation. Just what the functions of the organs of
the ear sacs are is not certainly known. These facts are of importance
when we consider the attempts made by Alexander and Kreidl to correlate
the various peculiarities of behavior shown by the dancer with the
structural facts which their work has revealed. This correlation is
indicated schematically below. The physiological facts to be accounted for
in terms of structure are presented in the first column, and the
anatomical facts which are thought to be explanatory, in the second (2 p.
539).
FUNCTION
1 Lack of sensitiveness to auditory stimuli. {Structure 1,2,3 below}
2 Defective equilibrational ability. {Structure 4,5,6 below}
3 Lack of turning dizziness. {Structure 4,5,6 below}
4 Normal reactions to galvanic stimulation. (not related in table to any
Structure)
STRUCTURE
1 Destruction of the papilla basilaris cochleae, etc.
2 Diminution of the inferior branch of the eighth nerve.
3 Marked degeneration of the ganglion spirale.
4 Destruction of the macula sacculi.
5 Diminution of the branches and roots of the superior and middle branches
of the eighth nerve.
6 Diminution of both ganglia vestibulii and of the nerve cells.
Alexander and Kreidl themselves believe that the partial deafness of the
dancers (for they admit that the total lack of hearing has not been
satisfactorily proved) is due to the defective condition of the cochlea.
They account for the imperfect equilibrational ability of the animals by
pointing out the structural peculiarities of the sacculus, the vestibular
ganglia, and the peripheral nerves. Similarly, the lack of dizziness they
suppose to be due to the diminution of the fibers of the nerves which
supply the canal organs, the atrophied condition of the vestibular
ganglia, and a disturbance of the peripheral sense organs. Furthermore,
there are no anatomical facts which would indicate a lack of galvanic
dizziness (2 p. 552).
Despite the fact that they seem to explain all the functional
peculiarities of the dancer, the statements made by Alexander and Kreidl
are neither satisfying nor convincing. Their statements concerning the
structure of the ear have not been verified by other investigators, and
their correlation of structural with functional facts lacks an
experimental basis.
In this connection it may be worth while to mention that a beautiful
theory of space perception which Cyon (9) had constructed, largely on the
basis of the demonstration by Rawitz that the dancers have only one normal
canal, is totally destroyed by Panse, Baginsky, Alexander and Kreidl, and
Kishi, for all of these observers found in the dancer three canals of
normal shape. Cyon had noted that the most abnormal of the voluntary as
well as of the forced movements of the dancer occur in the plane of the
canal which Rawitz found to be most strikingly defective. This fact he
connected with his observation that the fish Petromyzon, which possesses
only two canals, moves in only two spatial dimensions. The dancer with
only one functional canal in each ear moves in only one plane, and neither
it nor Petromyzon is able to move far in a straight line (11 p. 444). From
these and similar surmises, which his eagerness to construct an ingenious
theory led him to accept as facts quite uncritically, Cyon concluded that
the perception of space depends upon the number and arrangement of the
semicircular canals, and that the dancer behaves as it does because it
possesses canals of unusual shape and relations to one another. The
absurdity of Cyon's position becomes obvious when it is shown that the
structural conditions of which he was making use do not exist in the
dancer.
The results obtained by Kishi in his study of the ear of the dancer differ
in many important respects from those of all other investigators, but
especially from those of Rawitz and Alexander and Kreidl.
Kishi's work was evidently done with admirable carefulness. His methods in
the preparation of his materials, so far as can be judged from his report,
were safe and satisfactory, and his descriptions of results are minute and
give evidence of accuracy and conscientious thoughtfulness. The material
for his histological work he obtained from three different animal dealers.
It consisted of fifteen adult and nineteen young dancers, and, as material
for comparison, ten common gray mice. The animals were studied first
biologically, that their habits and behavior might be described accurately
and so far as possible accounted for in the light of whatever histological
results might be obtained subsequently; then they were studied
physiologically, that the functional importance of various organs which
would naturally be supposed to have to do with the peculiarities of the
mouse might be understood; and, finally, they were killed and their ears
and portions of their brains were studied microscopically, that structural
conditions for the biological and physiological facts might be discovered.
The ear, which was studied by the use of several series of sections, as
well as in gross dissections, is described by Kishi under three
headings:--
(1) The sound-receiving apparatus (auditory organs).
(2) The static apparatus (equilibrational organs).
(3) The sound-transmitting apparatus (ear drum, ear bones, etc.).
The chief results of his structural investigation may be stated briefly
under these three headings. In the sound-receiving or auditory apparatus,
Kishi failed to find the important deviations from the usual structure of
the mammalian ear which had been described by Rawitz. The latter
distinctly says that although the organ of Corti is present in all of the
whirls of the cochlea, the auditory cells in it are noticeably degenerate.
Kishi does not agree with Panse's statement (21 p. 476) that the auditory
organ of the dancer differs in no important respects from that of the
common mouse, for he found that in certain regions the hair cells of the
organ of Corti were fewer and smaller in the dancer. He therefore
concludes that the auditory organ is not entirely normal, but at the same
time he emphasizes the serious discrepancy between his results and those
of Rawitz. In not one of the ears of the twelve dancers which he studied
did Kishi find the direct communication between the utriculus and the
scala tympani which Rawitz described, and such differences as appeared in
the organ of Corti were in the nature of slight deviations rather than
marked degenerations.
In the outer wall of the ductus cochlearis of the dancer the stria
vasculosa is almost or totally lacking, while in the gray mouse it is
prominent. This condition of the stria vasculosa Kishi was the first to
notice in the dancer; Alexander and Kreidl had previously described a
similar condition in an albino cat. If, as has been supposed by some
physiologists, the stria vasculosa is really the source of the endolymph,
this state of affairs must have a marked influence on the functions of the
auditory apparatus and the static apparatus, for pressure differences
between the endolymph and the perilymph spaces must be present. And, as
Kishi points out, should such pressure differences be proved to exist, the
functional disturbance in the organ of hearing which the lack of responses
to sounds seems to indicate might better be ascribed to them than to the
streaming of the endolymph from the canals into the cochlea as assumed by
Rawitz (21 p. 477). Kishi merely suggests that the condition of the stria
may account for the deafness of the mouse; he does not feel at all
confident of the truth of his explanation, and he therefore promises in
his first paper a continuation of his work in an investigation of the
functions of the stria. This, however, he seems not to have accomplished
thus far.
[Illustration: FIGURE 12.--The inner ear of the dancer. Reproduced from
Kishi's figure in the _Zeitschrift für wissenschaftliche Zoölogie_, Bd.
71. _c.c._ crus simplex; o.b. anterior vertical canal; _h.b._ posterior
vertical canal; _a.b._ horizontal canal.]
The static apparatus Kishi describes as closely similar in form to that of
the gray mouse. In none of his twelve preparations of the ear of the
dancer did he find such abnormalities of form and connections in the
semicircular canals as Rawitz's figures and descriptions represent. Rawitz
states that the anterior canal is normal except in its lack of connection
with the posterior and that the posterior and horizontal are much reduced
in size. Kishi, on the contrary, insists that all of the three canals are
normal in shape and that the usual connection between the anterior and the
posterior canals, the crus simplex, exists. He justifies these statements
by presenting photographs of two dancer ears which he carefully removed
from the head. Comparison of these photographs (Figures 12 and 13) with
Rawitz's drawings of the conditions of the canals and sacs as he found
them (Figures 8, 9, and 10), and of both with the condition in the typical
mammalian ear as shown by Figure 7, will at once make clear the meaning of
Kishi's statements. That Rawitz's descriptions of the canals are not
correct is rendered almost certain by the fact that Panse, Baginsky,
Alexander and Kreidl, and Kishi all agree in describing them as normal in
form.
The only important respects in which Kishi found the membranous labyrinth,
that is, the canals and the ear sacs, of the dancer to differ from that of
the gray mouse are the following. In the dancer the cupola of the crista
acustica is not so plainly marked and not so highly developed, and the
raphae of the ampullae and canals, which frequently are clearly visible in
the gray mouse, are lacking (21 p. 478).
[Illustration: FIGURE 13.--The inner ear of the dancer, showing the spiral
form of the cochlea. After Kishi.]
The sound-transmitting apparatus of the dancer, according to Kishi,
differs only very slightly from that of the gray mouse, and there is no
reason to consider the differences which appear as important (21 p. 478).
Almost as amusing as the way in which Cyon's theory of space perception
disappears in the light of critical research is Panse's explanation of the
deafness of the dancer. Failing to find any defects in the auditory
apparatus of the inner ear which seemed adequate to account for the
obvious lack of responsiveness to sounds, this investigator concluded that
plugs of wax which he had noticed in the auditory meatus of the dancer
excluded sounds or in some way interfered with the functioning of the
tympanic membrane. Kishi reports that he found such plugs of wax in the
ears of one gray mouse, but in none of the dancers which he examined did
he discover them (21 p. 479). Panse's explanation of the defective hearing
of the dancer neither needs nor deserves further comment.
As one result of his investigation, Kishi is convinced that the dance
movements are not due to peculiarities in the semicircular canals and
their sense organs, as Rawitz claimed, for the general form and finer
structure of these organs in the dancer is practically the same as in the
common mouse. Kishi is just as certain that the whirling is not due to
defects in the canal organs, as Rawitz is that it is due to such
structural conditions! It is rather surprising that any one should feel
confident of the power of the microscope to reveal all those structural
conditions which are important as conditions of function. Probably there
are histological differences between the ear of the dancer and that of the
gray mouse, which, although undetectable by scientific means at present,
furnish the structural basis for the marked differences in behavior. As
has been set forth already (p. 9), Kishi accounts for the dance movements
by assuming the inheritance of an acquired character of behavior. This
inherited tendency to dance, he thinks, has been accentuated by the
confinement of the mice in narrow cages and their long-continued movement
in the wheels which are placed in the cages (21 p. 481).
Rawitz, Cyon, and Alexander and Kreidl felt themselves under the necessity
of finding peculiarities of behavior in the dancer which could be referred
to the various abnormalities of structure which they had either seen or
accepted on faith; Kishi found himself in a very different predicament,
for he had on his hands the commonly accepted statement that the animals
are deaf, without being able to find any structural basis for this defect.
To avoid the difficulty he questions the existence of deafness! If
perchance they are deaf, he thinks that it is possibly because of the
defect in the stria vasculosa. This suggestion Kishi makes despite the
fact that our ignorance of the function of the stria renders it impossible
for us to do otherwise than guess at its relation to hearing.
We have now briefly reviewed the results of the various important
investigations of the behavior and structure of the dancer.
The observations of Cyon, Zoth, and the writer establish beyond doubt the
existence of important individual differences in behavior if not of
distinct divisions within the species of mouse, and the general results of
the several anatomical investigations make it seem highly probable that
the structure of the ear, as well as the externally visible structural
features of the animals, vary widely. Unfortunately, the lack of agreement
in the descriptions of the ear given by the different students of the
subject renders impossible any certain correlation of structural and
functional facts. That the whirling and the lack of dizziness and of
hearing have their structural bases no one doubts, but whether it is in
the brain itself, in the sense organs, or in the labyrinth, our knowledge
does not permit us to say. With this statement Rawitz, Cyon, and Alexander
and Kreidl would not agree, for they believe that they have discovered
structural peculiarities which fully explain the behavior of the dancer.
Panse and Kishi, on the other hand, contend that the ear gives no
structural signs of such peculiarities as the dancing and deafness
suggest; they therefore look to the cerebellum for the seat of the
disturbance. With the same possibility in mind the author of "Fancy
Varieties of Mice" writes: "These quaint little creatures make amusing
pets for any one who is not scientific, or very fond of knowing 'the
reason why.' In their case, the reason of the peculiarity which gives them
their name is rather a sad one. It is now pretty conclusively established
that they are no more Japanese than they are of any other country in
particular, but that the originators of the breed were common fancy mice
which were suffering from a disease of the brain analogous to the 'gid' in
sheep. In the latter, the complaint is caused by a parasite in the brain;
in the case of the Waltzing Mouse, it is probably due to an hereditary
malformation therein. Be this as it may, the breed is now a firmly
established one, and the children of waltzing mice waltz like their
parents" (32 p. 45). Although it is quite possible that peculiarities in
the central nervous system, rather than in the peripheral nervous system,
may be responsible for the forms of behavior exhibited by the dancer, it
must be remembered that no such peculiarities have been revealed by the
examination of the central nervous system. The old fancier has neither
better nor worse grounds for his belief than have Panse and Kishi.
So far as the reliability of the anatomical work which has been discussed
is in question, it would seem that Rawitz's results are rendered somewhat
unsatisfactory by the carelessness of Cyon in fixing the materials; that
Panse's descriptions and comparisons are neither careful nor detailed
enough to be convincing; that the work of Alexander and Kreidl, as well as
that of Kishi, gives evidence of accuracy and trustworthiness. The fact
that the statements of Alexander and Kreidl frequently do not agree with
those of Kishi proves that there are serious errors in the work of one or
another of these investigators. Cyon's discussion of the anatomy of the
dancer is not to be taken too seriously, for by his theory of space
perception and of a sixth sense he was unduly biased in favor of the
structural peculiarities described by Rawitz. Nevertheless, his discussion
is not without interest, for the way in which he succeeded in making every
structural fact which Rawitz suggested fit into his theories and help to
account for the functional peculiarities which he had himself observed, is
extremely clever and indicates a splendid scientific imagination.
To sum up: All the facts of behavior and physiology which have been
established lead us to expect certain marked structural differences
between the dancer and the common mouse. The bizarre movements, lack of
equilibrational ability, and the nervous shaking of the head suggest the
presence of peculiar conditions in the semicircular canals or their sense
organs; and the lack of sensitiveness to sounds indicates defects in the
cochlea. Yet, strange as it may seem to those who are not familiar with
the difficulties of the study of the minute structure of these organs, no
structural conditions have been discovered which account satisfactorily
for the dancer's peculiarities of behavior. That the ear is unusual in
form is highly probable, since three of the four investigators who have
studied it carefully agree that it differs more or less markedly from that
of the common mouse. But, on the other hand, the serious lack of agreement
in their several descriptions of the conditions which they observed
renders their results utterly inconclusive and extremely unsatisfactory.
The status of our knowledge of the structure of the central nervous system
is even less satisfactory, if possible, than that of our knowledge of
those portions of the peripheral nervous system which would naturally be
supposed to have to do with such functional peculiarities as the dancer
exhibits. So far as I have been able to learn, no investigator has
carefully examined the brain and spinal cord in comparison with those of
the common mouse, and only those who have failed to find any structural
basis for the facts of behavior in the organs of the ear have attempted to
account for the dancer's whirling and deafness by assuming that the
cerebellum is unusual in structure. We are, therefore, forced to conclude
that our knowledge of the nervous system of the dancing mouse does not at
present enable us to explain the behavior of the animal.
It seems highly probable to me, in the light of my observation of the
dancer and my study of the entire literature concerning the animal, that
no adequate explanation of its activities can be given in terms of the
structure of the peripheral or the central nervous system, or of both, but
that the structure of the entire organism will have to be taken into
account. The dancer's physiological characteristics, in fact, suggest
multitudinous structural peculiarities. I have confined my study to its
behavior, not because the problems of structure seemed less interesting or
less important, but simply because I found it necessary thus to limit the
field of research in order to accomplish what I wished within a limited
period.
That there are structural bases for the forms of behavior which this book
describes is as certain as it could be were they definitely known; that
they, or at least some of them, are discoverable by means of our present-
day histological methods is almost as certain. It is, therefore, obvious
that this is an excellent field for further research. It is not an
agreeable task to report inconclusive and contradictory results, and I
have devoted this chapter to a brief account of the work that has been
done by others on the structure of the ear of the dancer rather for the
sake of presenting a complete account of the animal as it is known to-day
than because of the value of the facts which could be stated.
CHAPTER VI
THE SENSE OF HEARING
Repeatedly in the foregoing chapters mention has been made of the dancer's
irresponsiveness to sounds, but it has not been definitely stated whether
this peculiarity of behavior is due to deafness or to the inhibition of
reaction. This chapter is concerned with the evidence which bears upon the
problem of the existence of a sense of hearing. Again I may be permitted
to call attention to the observations of other investigators before
presenting the results of my own experiments and stating the conclusions
which I have reached through the consideration of all available facts.
By the results of various simple tests which he made, Rawitz (25 p. 238)
was convinced that the adult dancer is totally deaf. He did not experiment
with the young, but he says he thinks they may be able to hear, since the
necessary structural conditions are present. This guess which Rawitz made
on the basis of very indefinite and uncertain knowledge of the histology
of the ear of the young dancer is of special interest in the light of
facts revealed by my own experiments. Unfortunately the study of hearing
made by Rawitz is casual rather than thorough, and although it may turn
out that all of his statements are justified by his observations, the
reader is not likely to get much satisfaction from his discussion of the
subject.
Inasmuch as he could discover no structural basis for deafness, Panse (23
p. 140) expressed himself as unwilling to believe that the mice are deaf,
and this despite the fact that he observed no responses to the sounds made
by a series of tuning forks ranging from C5 to C8. He believes rather that
they are strangely irresponsive to sounds and that their sensitiveness is
dulled, possibly, by the presence of plugs of wax in the ears. Since
another investigator, Kishi, has observed the presence of similar plugs of
wax in the ears of common mice which could hear, there is but slight
probability that Panse is right in considering the plugs of wax as the
cause of the dancer's irresponsiveness to sounds.
Far more thoroughgoing tests than those of Rawitz or Panse were made by
Cyon (9 p. 218), who holds the unique position of being the only person on
record who has observed the adult dancer give definite reactions to
sounds. To a König Galton whistle so adjusted that it gave a tone of about
7000 complete vibrations per second, which is said to be about the pitch
of the voice of the dancer, some of the animals tested by Cyon responded
unmistakably, others not at all. In one group of four mice, two not only
reacted markedly to the sound of the whistle but apparently listened
intently, for as soon as the whistle was blown they ran to the side of the
cage and pressed their noses against the walls as if attempting to
approach the source of the stimulus. The remaining two mice gave not the
slightest indication that the sound acted as a stimulus. By the repetition
of this sound from eight to twelve times Cyon states that he was able to
arouse the mice from sleep. When thus disturbed, the female came out of
the nest box before the male. Similarly when the mice were disturbed by
the whistle in the midst of their dancing, the female was first to retreat
into the nest box. There is thus, according to Cyon, some indication of
sex, as well as individual, differences in sensitiveness to the sound of
the whistle. Cyon's statement that in order to evoke a response the
whistle must be held above the head of the dancer suggests at once the
possibility that currents of air or odors instead of sounds may have been
responsible for the reactions which he observed. The work of this
investigator justifies caution in the acceptance of his statements.
Neither the conditions under which the auditory tests were made nor the
condition of the animals is described with sufficient accuracy to make
possible the comparison of Cyon's work with that of other investigators.
As will appear later, it is of the utmost importance that the influence of
other stimuli than sound be avoided during the tests and that the age of
the mouse be known. The conclusion reached by Cyon is that some dancers
are able to hear sounds of about the pitch of their own cries.
The fact, emphasized by Cyon, that the mice respond to tones of about the
pitch of their own voice is of peculiar interest in its relation to the
additional statements made by the same author to the effect that the
female dancer is more sensitive to sounds than the male, and that the
males either do not possess a voice or are much less sensitive to
disagreeable stimuli than the females. In the case of the dancers which he
first studied (9 p. 218), Cyon observed that certain strong stimuli evoked
pain cries; but later in his investigation he noticed that four
individuals, all of which were males, never responded thus to disagreeable
stimulation (11 p.431). He asks, therefore, does this mean that the males
lack a voice or that they are less sensitive than the females? The fact
that he did not succeed in getting a definite answer to this simple
question is indicative of the character of Cyon's work. My dancers have
provided me with ample evidence concerning the matter. Both the males and
the females, among the dancers which I have studied, possess a voice.
The females, especially during periods of sexual excitement, are much more
likely to squeak than the males. At such times they give their shrill cry
whenever they are touched by another mouse or by the human hand. A slight
pinching of the tail will frequently cause the female to squeak, but the
male seldom responds to the same stimulus by crying out. The most
satisfactory way to demonstrate the existence of a voice in the male is to
subject him to the stimulating effect of an induced current, so weak that
it is barely appreciable to the human hand. To this unexpected stimulus
even the male usually responds by a sudden squeak. There can be no doubt,
then, of the possession of a voice by both males and females. The males
may be either less sensitive or less given to vocal expression, but they
are quite able to squeak when favorable conditions are presented. The
possession of a voice by an animal is presumptive evidence in favor of a
sense of hearing, but it would scarcely be safe to say that the mice must
be able to hear their own voices. Cyon, however, thinks that some dancers
can. What further evidence is to be had?
Although they obtained no visible motor reactions to such noises as the
clapping of the hands, the snapping of the fingers, or to the tones of
tuning forks of different pitches and the shrill tones of the Galton
whistle, Alexander and Kreidl (1 p. 547) are not convinced of the total
deafness of the dancer, for, as they remark, common mice which undoubtedly
hear do not invariably respond visibly to sounds. Furthermore, the
anatomical conditions revealed by their investigation of the ear of the
dancer are not such as to render sensitiveness to sounds impossible. They
recognize also that the existence of the ability to produce sounds is an
indication of hearing. They have no confidence in the results reported by
Cyon, for they feel that he did not take adequate precautions to guard
against the action of other than auditory stimuli.
Zoth (31 p. 170) has pointed out with reason and force that testing the
sensitiveness of the mice is especially difficult because of their
restlessness. They are almost constantly executing quick, jerky movements,
starting, stopping, or changing the direction of movement, and it is
therefore extremely difficult to tell with even a fair degree of certainty
whether a given movement which occurs simultaneously with a sound is a
response to the sound or merely coincident with it. With great care in the
exclusion of the influence of extraneous stimuli, Zoth tried a large
number of experiments to test the hearing of both young and adult dancers.
Not once did he observe an indubitable auditory reaction. As he says, "I
have performed numerous experiments with the Galton whistle, with a
squeaking glass stopper, with caps and cartridges, without being able to
come to any certain conclusion. With reference to the Galton whistle and
particularly to the tone which was said to have been heard extremely well
by Cyon's mice, I believe I am rather safe in asserting that my mice,
young (12-13 days) as well as old, do not react to the König Galton
whistle (7210 Vs.). They could not be awakened out of sleep by repetitions
of the sound, nor enticed out of their nests, and their dancing could not
be interrupted" (31 p. 170). Zoth's experiments appear to be the most
careful and critical of those thus far considered.
Last to be mentioned, but in many respects of greatest interest and value,
is the work of Kishi (21 p. 482) on the problem of hearing. To this acute
observer belongs the credit of calling attention emphatically to the ear
movements which are exhibited by the dancer. Frequently, as he remarks,
the ears move as if the animal were listening or trying to determine the
direction whence comes a sound, yet usually the mouse gives no other sign
of hearing. That the absence of ordinary reactions to sounds is due to
deafness, Kishi, like Panse, is led to doubt because his anatomical
studies have not revealed any defects in the organs of hearing which would
seem to indicate the lack of this sense.
This historical survey of the problem of hearing has brought out a few
important facts. No one of the several investigators of the subject, with
the exception of Cyon, is certain that the dancer can hear, and no one of
them, with the exception of Rawitz, is certain that it cannot hear! Cyon
almost certainly observed two kinds of dancing mice. Those of his dancers
which exhibited exceptional ability to climb in the vertical direction and
which also gave good evidence of hearing certain sounds may have been
hybrids resulting from the crossing of the dancer with a common mouse, or
they may have been exceptional specimens of the true dancer variety. A
third possibility is suggested by Rawitz's belief in the ability of the
young dancer to hear. Cyon's positive results may have been obtained with
immature individuals. I am strongly inclined to believe that Cyon did
observe two types of dancer, and to accept his statement that some of the
mice could hear, whereas others could not. It is evident, in the light of
our examination of the experimental results thus far obtained by other
investigators, that neither the total lack of sensitiveness to sounds in
the adult nor the presence of such sensitiveness in the young dancer has
been satisfactorily proved.
I shall now report in detail the results of my own study of the sense of
hearing in the dancer. As the behavior of the young differs greatly from
that of the adult, by which is meant the sexually mature animal, I shall
present first the results of my experiments with adults and later, in
contrast, the results obtained with mice from one to twenty-eight days
old.
My preliminary tests were made with noises. While carefully guarding
against the interference of visual, tactual, temperature, and olfactory
stimuli, I produced noises of varying degrees of loudness by clapping the
hands together suddenly, by shouting, whistling, exploding pistol caps,
striking steel bars, ringing an electric bell, and causing another mouse
to squeak. To these sounds a common mouse usually responds either by
starting violently, or by trembling and remaining perfectly quiet for a
few seconds, as if frightened. The adult dancers which I have tested, and
I have repeated the experiment scores of times during the last three years
with more than a hundred different individuals, have never given
unmistakable evidence of hearing. Either they are totally deaf or there is
a most surprising lack of motor reactions.
Precisely the same results were obtained in tests made with the Galton
whistle throughout its range of pitches, and with Appuun whistles which,
according to their markings, ranged from 2000 Vs. (C_4) to 48,000 (G_9),
but which undoubtedly did not correspond at all exactly to this range, and
with a series of König tuning forks which gave tones varying in pitch from
1024 to 16,382 complete vibrations.
I am willing to trust these experimental results the more fully because
during all the time I have had adult dancers under observation I have
never once seen a reaction which could with any fair degree of certainty
be referred to an auditory stimulus. Never once, although I have tried
repeatedly, have I succeeded in arousing a dancer from sleep by producing
noises or tones, nor have I ever been able to observe any influence of
sounds on the dance movements. All of Cyon's signs have failed with my
mice. Occasionally what looked like a response to some sound appeared, but
critical observation invariably proved it to be due to some other cause
than the auditory stimulus. A sound produced above the animal is very
likely to bring about a motor reaction, as Cyon claims; but I have always
found it to be the result of the currents of air or odors, which usually
influence the animal when the experimenter is holding any object above it.
I do not wish to maintain that Cyon's conclusions are false; I merely
emphasize the necessity for care in the exclusion of other stimuli. The
mice are extremely sensitive to changes in temperature, such, for example,
as are produced by the breath of the experimenter, and one must constantly
guard against the misinterpretation of behavior.
In a single experiment with mice over a month old, I observed what might
possibly indicate sensitiveness to sound. While holding a mouse, thirty-
five days old, in my hand I pursed my lips and made a very shrill sound by
drawing in air; the mouse seemed to start perceptibly according to the
indications given by my sense of touch. I repeated the stimulus several
times and each time I could see and feel the animal start slightly. With
two other individuals which I tested the reaction was less certain, and
with several others I failed to get any indication of response. This would
seem to prove that the three individuals which responded happened to be
sensitive to that particular tone at the age of five weeks. The test is
unsatisfactory because the vibrations from my own body may have brought
about the reaction instead of the air vibrations produced by my lips, and
I therefore merely mention it in the enumeration of the various
experimental tests which I have made.
If we should conclude from all the negative evidence that is available, or
that could be obtained, that the dancer is totally deaf, it might fairly
be objected that the conclusion is unsafe, since an animal does not
necessarily respond to stimuli by a visible change in the position or
relations of its body. Death feigning may fairly be considered a response
to a stimulus or stimulus complex, yet there may be no sign of movement.
The green frog when observed in the laboratory usually gives no indication
whatever, by movements that are readily observable, that it hears sounds
which occur about it, but I have been able to show by means of indirect
methods of study that it is stimulated by these same sounds.[1] Its rate
of respiration is changed by the sounds, and although a sound does not
bring about a bodily movement, it does very noticeably influence movements
in response to other stimuli which occur simultaneously with the sound. I
discovered that under certain rather simple experimental conditions the
green frog would regularly respond to a touch on the back by drawing its
hind leg up toward the body. Under the same conditions the sound of an
electric bell caused no visible movement of the leg, but if at the instant
the back was touched the bell was rung, the leg movement was much greater
than that brought about by the touch alone. This suggests at once the
desirability of studying the sense of hearing in the dancer by some
indirect method. The animal may be stimulated, and yet it may not give any
visible sign of the influence of the auditory stimulus.
[Footnote 1: "The Sense of Hearing in Frogs." _Journal of Comparative
Neurology and Psychology_, Vol. XV, p. 288, 1905.]
Were not the dancing so extremely variable in rapidity and duration, it
might be used as an index of the influence of auditory stimuli. Cyon's
statements would indicate that sounds interfere with the dancing, but as I
obtained no evidence of this, I worked instead with the following indirect
method, which may be called the method of auditory choice.
The apparatus which was used is described in detail in Chapter VII.
Figures 14 and 15 will greatly aid the reader in understanding its
essential features. Two small wooden boxes, identical in form and as
closely similar as possible in general appearance, were placed in a larger
box in such positions that a mouse was forced to enter and pass through
one of them in order to get to the nest-box. On the bottom of each of
these small boxes was a series of wires through which an electric current
could be made to pass at the will of the experimenter. The boxes could
readily be interchanged in position. At one side of the large wooden box
and beyond the range of vision of the mouse was an electric bell which
could be caused to ring whenever the mouse approached the entrance to one
of the small boxes. The point of the experiment was to determine whether
the dancer could learn to avoid the box-which-rang when it was approached.
The method of conducting the tests was as follows. Each day at a certain
hour the mouse was placed in that part of the large box whence it could
escape to the nest-box only by passing through one of the small boxes. If
it approached the wrong box (whether it happened to be the one on the
right or the one on the left depended upon the experimenter's decision),
the bell began to ring as a warning against entering; if it approached the
other box, all was silent. As motives for the choice of the box-which-did-
not-ring both reward and punishment were employed. The reward consisted of
freedom to return to the nest-box _via_ the passage which led from the
box-which-did-not-ring; the punishment, which consisted of a disagreeable
electric shock, was given whenever the mouse entered the wrong box, that
is, the one which had the sound as a warning. Entering the wrong box
resulted in a disagreeable stimulus and in the necessity of returning to
the large box, for the exit to the nest-box by way of the passage from
this box was closed. My assumption, on the basis of extended study of the
ability of the dancer to profit by experience, was that if it could hear
the sound of the bell it would soon learn to avoid the box-that-rang and
enter instead the one which had no sound associated with it.
Systematic tests were made with No. 4 from the 3d to the 12th of February,
inclusive, 1906. Each day the mouse was permitted to find his way to the
nest-box through one of the small boxes ten times in succession. Usually
the experimenter rang the bell alternately for the box on the left and the
box on the right. The time required for such a series of experiments
varied, according to the rapidity with which the mouse made his choice,
from ten to thirty minutes. If in these experiments the animal approached
and entered the right, or soundless box, directly, the choice indicated
nothing so far as ability to hear is concerned; if it entered the wrong,
or sounding box, despite the ringing of the bell, it indicated either the
lack of the influence of experience or inability to hear the sound; but if
it regularly avoided the box-which-sounded it thus gave evidence of
ability to hear the sound of the bell. The purpose of the test was to
determine, not whether the mouse could learn, but whether it could hear.
For ten successive days this experiment was carried on with No. 4 without
the least indication of increasing ability to avoid the wrong box by the
association of the sound of the bell with the disagreeable electric shock
and failure to escape to the nest-box. In fact, the experiment was
discontinued because it became evident that an impossible task had been
set for the mouse. Day by day as the tests were in progress I noticed that
the animal became increasingly afraid of the entrances to the small boxes;
it seemed absolutely helpless in the face of the situation. Partly because
of the definiteness of the negative results obtained with No. 4 and partly
because of the cruelty of subjecting an animal to disagreeable conditions
which it is unable to avoid, the experiment was not repeated with other
individuals. I have never conducted an experiment which gave me as much
discomfort as this; it was like being set to whip a deaf child because it
did not learn to respond to stimuli which it could not feel.
By a very similar method No. 18 was tested for his sensitiveness to the
noise and jar from the induction apparatus which was used in connection
with many of my experiments on vision and the modifiability of behavior.
In this experiment the wrong box was indicated by the buzzing sound of the
apparatus and the slight vibrations which resulted from it. Although No.
18 was tested, as was No. 4, for ten successive days, ten trials each day,
it gave no evidence of ability to avoid the box-which-buzzed.
Since both direct and indirect methods of testing the hearing of the
dancer have uniformly given negative results, in the case of mice more
than five weeks old, I feel justified in concluding that they are totally
deaf and not merely irresponsive to sounds.
Rawitz's statements, and the fact that what may have been auditory
reactions were obtained with a few individuals of five weeks of age,
suggest that the mice may be able to hear at certain periods of life. To
discover whether this is true I have tested the young of twenty different
litters from the first day to the twenty-eighth, either daily or at
intervals of two or three days. In these tests König forks, steel bars,
and a Galton whistle were used. The results obtained are curiously
interesting.
During the first two weeks of life none of the mice which I tested gave
any visible motor response to the various sounds used. During the third
week certain of the individuals responded vigorously to sudden high tones
and loud noises. After the third week I have seen only doubtful signs of
hearing. I shall now describe in detail the method of experimentation, the
condition of the animals, and the nature of the auditory reactions.
Between the twelfth and the eighteenth day the auditory canal becomes open
to the exterior. The time is very variable in different litters, for their
rate of growth depends upon the amount of nourishment which the mother is
able to supply. Without exception, in my experience, the opening to the
ear appears before the eyes are open. Consequently visual stimuli usually
are not disturbing factors in the auditory tests with mice less than
sixteen days old. There is also a sudden and marked change in the behavior
of the mice during the third week. Whereas, for the first fourteen or
eighteen days they are rather quiet and deliberate in their movements when
removed from the nest, some time in the third week their behavior suddenly
changes and they act as if frightened when taken up by the experimenter.
They jump out of his hand, squeak, and sometimes show fight. This is so
pronounced that it has attracted my attention many times and I have
studied it carefully to determine, if possible, whether it is due to some
profound change in the nervous system which thus suddenly increases the
sensitiveness of the animal or to the development of the sexual organs. I
am inclined to think that it is a nervous phenomenon which is intimately
connected with the sexual condition. Within a day or two after it appears
the mice usually begin to show auditory reactions and continue to do so
for three to five days.
I shall now describe the results obtained with a few typical litters. A
litter born of Nos. 151 and 152 gave uniformly negative results in all
auditory tests up to the fourteenth day. On that day the ears were open,
and the following observations were recorded. The five individuals of the
litter, four females and one male, were taken from the nest one at a time
at 7 A.M. and placed on a piece of paper in the bright sunlight. The
warmth of the sun soon quieted them so that auditory tests could be made
to advantage. As soon as an individual had become perfectly still, the
Galton whistle was held at a distance of about four inches from its head
in such a position that it could not be seen nor the currents of air
caused by it felt, and suddenly blown. Each of the five mice responded to
the first few repetitions of this stimulus by movements of the ears,
twitchings of the body, and jerky movements of the legs. The most violent
reactions resulted when the individual was lying on its back with its legs
extended free in the air. Under such circumstances the four legs were
often drawn together suddenly when the whistle was sounded. Similar
responses were obtained with the lip sound already mentioned. Two other
observers saw these experiments, and they agreed that there can be no
doubt that the mice responded to the sound. The sounds which were
effective lay between 5000 and 10,000 complete vibrations.
On the fifteenth day the eyes were just beginning to open. Three of the
mice responded definitely to the sounds, but the other two slightly, if at
all. On the sixteenth day they were all too persistently active for
satisfactory auditory tests, and on the seventeenth, although they were
tested repeatedly under what appeared to be favorable conditions, no signs
of sensitiveness were noted. Although I continued to test this litter, at
intervals of three or four days, for two weeks longer, I did not once
observe a response to sound.
This was the first litter with which I obtained perfectly definite, clear-
cut responses to sounds. That the reactive ability had not been present
earlier than the fourteenth day I am confident, for I had conducted the
tests in precisely the same manner daily up to the time of the appearance
of the reactions. To argue that the mice heard before the fourteenth day,
but were unable to react because the proper motor mechanism had not
developed sufficiently would be short-sighted, for if the response
depended upon the development of such a mechanism, it is not likely that
it would disappear so quickly. I am therefore satisfied that these
reactions indicate hearing.
With another litter the following results were obtained. On the thirteenth
day each of the eight members of the litter responded definitely and
uniformly to the Galton whistle, set at 5 (probably about 8000 complete
vibrations), and to a König steel bar of a vibration rate of 4096 Vs. The
largest individuals, for almost always there are noticeable differences in
size among the members of a litter, appeared to be most sensitive to
sounds.
On the fifteenth day and again on the seventeenth unmistakable responses
to sound were observed; on the eighteenth the responses were indefinite,
and on the nineteenth none were obtained. I continued the tests up to the
twenty-eighth day without further indications of hearing.
Certain individuals in this litter reacted so vigorously to the loud sound
produced by striking the steel bar a sharp blow and also to the Galton
whistle, during a period of five days, that I have no hesitation in saying
that they evidently heard during that period of their lives. Other members
of the litter seemed to be less sensitive; their reactions were sometimes
so indefinite as to leave the experimenter in doubt about the presence of
hearing.
A third litter, which developed very slowly because of lack of sufficient
food, first showed unmistakable reactions to sound on the twenty-first
day. On this day only two of the five individuals reacted. The reactions
were much more obvious on the twenty-second day, but thereafter they
became indefinite.
Still another litter, which consisted of one female and four males, began
to exhibit the quick, jerky movements, already mentioned, on the
fourteenth day. On the morning of the fifteenth day three members of the
litter definitely reacted to the tone of the steel bar, and also to the
hammer blow when the bar was held tightly in the hand of the experimenter.
My observations were verified by another experimenter. Two individuals
which appeared to be very sensitive were selected for special tests. Their
reactions were obvious on the sixteenth, seventeenth, and eighteenth days;
on the nineteenth day they were indefinite, and on the twentieth none
could be detected. Some individuals of this litter certainly had the
ability to hear for at least five days.
A sixth litter of four females and two males first gave indications of the
change in behavior which by this time I had come to interpret as a sign of
the approach of the period of auditory sensitiveness, on the seventeenth
day. I had tested them almost every day previous to this time without
obtaining evidence of hearing. The tests with the steel bar and the Galton
whistle were continued each day until the end of the fourth week without
positive results. To all appearances the individuals of this litter were
unable to hear at any time during the first month of life.
Practically the same results were obtained with another litter of four
females. The change in their behavior was obvious on the eighteenth day,
but at no time during the first month did they give any satisfactory
indications of hearing.
In the accompanying table, I have presented in condensed form the results
of my auditory tests in the case of twelve litters of young dancers.
TABLE 5
PERIOD OF AUDITORY REACTION IN YOUNG DANCERS
PARENTS No. in Change in Ears Auditory Reactions
Litter Behavior Open Appear Disappear
152+151 5 13th day 14th day 14th day 16th day
152+15l 8 (?) 13th day 13th day 17th day
152+151 5 13th day 13th day 13th day 17th day
152+151 4 10th day 12th day 13th day 15th day
410+415 5 14th day 15th day 15th day 19th day
410+415 6 13th day 14th day 14th day 18th day
420+425 2 12th day 14th day 14th day 17th day
210+215 5 17th day 13th day 17th day 19th day
210+215 6 11th day 14th day No reactions
220+225 6 16th day 14th day No reactions
220+225 6 17th day 13th day No reactions
212+211 4 15th day 14th day No reactions
Certain of the litters tested responded definitely to sounds, others gave
no sign of hearing at any time during the first four weeks of life. Of the
twelve litters for which the results of auditory tests are presented in
Table 5, eight evidently passed through an auditory period. It is
important to note that all except one of these were the offspring of Nos.
151 and 152, or of their descendants Nos. 410 and 415 and Nos. 420 and
425. In fact every one of the litters in this line of descent which I have
tested, and they now number fifteen, has given indications of auditory
sensitiveness. And, on the other hand, only in a single instance have the
litters born of Nos. 210 and 215, or of their descendants, given evidence
of ability to hear.
These two distinct lines of descent may be referred to hereafter as the
400 and the 200 lines. I have observed several important differences
between the individuals of these groups in addition to the one already
mentioned. The 200 mice were sometimes gray and white instead of black and
white; they climbed much more readily and danced less vigorously than
those of the 400 group. These facts are particularly interesting in
connection with Cyon's descriptions of the two types of dancer which he
observed.
In criticism of my conclusion that the young dancers are able to hear
certain sounds for a few days early in life, and then become deaf, it has
been suggested that they cease to react because they rapidly become
accustomed to the sounds. That this is not the case, is evident from the
fact that the reactions often increase in definiteness during the first
two or three days and then suddenly disappear entirely. But even if this
were not true, it would seem extremely improbable that the mouse should
become accustomed to a sudden and startlingly loud sound with so few
repetitions as occurred in these tests. On any one day the sounds were not
made more than five to ten times. Moreover, under the same external
condition, the common mouse reacts unmistakably to these sounds day after
day when they are first produced, although with repetition of the stimulus
at short intervals, the reactions soon become indefinite or disappear.
The chief results of my study of hearing in the dancer may be summed up in
a very few words. The young dancer, in some instances, hears sounds for a
few days during the third week of life. The adult is totally deaf. Shortly
before the period of auditory sensitiveness, the young dancer becomes
extremely excitable and pugnacious.
CHAPTER VII
THE SENSE OF SIGHT: BRIGHTNESS VISION
The sense of sight in the dancer has received little attention hitherto.
In the literature there are a few casual statements to the effect that it
is of importance. Zoth, for example (31 p. 149), remarks that it seems to
be keenly developed; and other writers, on the basis of their observation
of the animal's behavior, hazard similar statements. The descriptions of
the behavior of blinded mice, as given by Cyon, Alexander and Kreidl, and
Kishi (p.47), apparently indicate that the sense is of some value; they do
not, however, furnish definite information concerning its nature and its
role in the daily life of the animal.
The experimental study of this subject which is now to be described was
undertaken, after careful and long-continued observation of the general
behavior of the dancer, in order that our knowledge of the nature and
value of the sense of sight in this representative of the Mammalia might
be increased in scope and definiteness. The results of this study
naturally fall into three groups: (1) those which concern brightness
vision, (2) those which concern color vision, and (3) those which indicate
the role of sight in the life of the dancer.
Too frequently investigators, in their work on vision in animals, have
assumed that brightness vision and color vision are inseparable; or, if
not making this assumption, they have failed to realize that the same
wave-length probably has markedly different effects upon the retinal
elements of the eyes of unlike organisms. In a study of the sense of sight
it is extremely important to discover whether difference in the quality,
as well as in the intensity, of a visual stimulus influences the organism;
in other words, whether color sensitiveness, as well as brightness
sensitiveness, is present. If the dancer perceives only brightness or
luminosity, and not color, it is evident that its visual world is
strikingly different from that of the normal human being. The experiments
now to be described were planned to show what the facts really are.
[Illustration: Figure 14.--Discrimination box. _W_, electric-box with
white cardboards; B, electric-box with black cardboards. Drawn by Mr. C.H.
Toll.]
As a means of testing the ability of the dancer to distinguish differences
in brightness, the experiment box represented by Figures 14 and 15 was
devised. Figure 14 is the box as seen from the position of the
experimenter during the tests. Figure 15 is its ground plan. This box,
which was made of wood, was 98 cm. long, 38 cm. wide, and 17 cm. deep, as
measured on the outside. The plan of construction and its significance in
connection with these experiments on vision will be clear from the
following account of the experimental procedure. A mouse whose brightness
vision was to be tested was placed in the nest-box, A (Figure 15). Thence
by pushing open the swinging door at _I_, it could pass into the entrance
chamber, _B_. Having entered _B_ it could return to _A_ only by passing
through one of the electric-boxes, marked _W_, and following the alley to
_O_, where by pushing open the swing door it could enter the nest-box. The
door at _I_ swung inward, toward _B_, only; those at _O_, right and left,
swung outward, toward _A_, only. It was therefore impossible for the mouse
to follow any other course than _A-I-B-L-W-E-O_ or _A-I-B-R-W-E-O_. The
doors at _I_ and _O_ were pieces of wire netting of 1/2 cm. mesh, hinged
at the top so that a mouse could readily open them, in one direction, by
pushing with its nose at any point along the bottom. On the floor of each
of the electric-boxes, _W_, was an oak board 1 cm. in thickness, which
carried electric wires by means of which the mouse could be shocked in _W_
when the tests demanded it. The interrupted circuit constituted by the
wires in the two electric-boxes, in connection with the induction
apparatus, _IC_, the dry battery, _C_, and the hand key, _K_, was made by
taking two pieces of No. 20 American standard gauge copper wire and
winding them around the oak board which was to be placed on the floor of
each electric-box. The wires, which ran parallel with one another, 1/2 cm.
apart, fitted into shallow grooves in the edges of the board, and thus, as
well as by being drawn taut, they were held firmly in position. The coils
of the two pieces of wire alternated, forming an interrupted circuit
which, when the key _K_ was closed, was completed if the feet of a mouse
rested on points of both pieces of wire. Since copper wire stretches
easily and becomes loose on the wooden base, it is better to use phosphor
bronze wire of about the same size, if the surface covered by the
interrupted circuit is more than three or four inches in width. The
phosphor bronze wire is more difficult to wind satisfactorily, for it is
harder to bend than the copper wire, and it has the further disadvantage
of being more brittle. But when once placed properly, it forms a far more
lasting and satisfactory interrupted circuit for such experiments as those
to be described than does copper wire. In the case of the electric-boxes
under consideration, the oak boards which carried the interrupted circuits
were separate, and the two circuits were joined by the union of the wires
between the boxes. The free ends of the two pieces of wire which
constituted the interrupted circuit were connected with the secondary coil
of a Porter inductorium whose primary coil was in circuit with a No. 6
Columbia dry battery. In the light of preliminary experiments, made in
preparation for the tests of vision, the strength of the induced current
received by the mouse was so regulated, by changing the position of the
secondary coil with reference to the primary, that it was disagreeable but
not injurious to the animal. What part the disagreeable shock played in
the test of brightness vision will now be explained.
[Illustration: FIGURE 15.--Ground plan of discrimination box. _A_, nest-
box; _B_, entrance chamber; _W,W_, electric-boxes; _L_, doorway of left
electric-box; _R_, doorway of right electric-box; _E_, exit from electric-
box to alley; _I_, swinging door between _A_ and _B_; _O_, swinging door
between alley and _A_; _IC_, induction apparatus; _C_, electric cell; _K_,
key in circuit.]
An opportunity for visual discrimination by brightness difference was
provided by placing dead black cardboard at the entrance and on the inside
of one of the electric-boxes, as shown in Figure 14, _B_, and white
cardboard similarly in the other box. These cardboards were movable and
could be changed from one box to the other at the will of the
experimenter. The test consisted in requiring the mouse to choose a
certain brightness, for example, the white cardboard side, in order to
return to the nest-box without receiving an electric shock. The question
which the experimenter asked in connection with this test really is, Can a
dancer learn to go to the white box and thus avoid discomfort? If we
assume its ability to profit by experience within the limits of the number
of experiences which it was given, such a modification of behavior would
indicate discrimination of brightness. Can the dancer distinguish white
from black; light gray from dark gray; two grays which are almost of the
same brightness? The results which make up the remainder of this and the
following chapter furnish a definite answer to these questions.
To return to the experimental procedure, the mouse which is being tested
is placed by the experimenter in the nest-box, where frequently in the
early tests food and a comfortable nest were attractions. If it does not
of its own accord, as a result of its abundant random activity, pass
through _I_ into _B_ within a few seconds, it is directed to the doorway
and urged through. A choice is now demanded of the animal; to return to
the nest-box it must enter either the white electric-box or the black one.
Should it choose the white box, it is permitted to return directly to _A_
by way of the doorway _E_, the alley, and the swinging door at _O_, and it
thus gets the satisfaction of unobstructed activity, freedom to whirl, to
feed, and to retreat for a time to the nest. Should it choose to attempt
to enter the black box, as it touches the wires of the interrupted circuit
it receives a shock as a result of the closing of the key in the circuit
by the experimenter, and further, if it continues its forward course
instead of retreating from the "stinging" black box, its passage through
_E_ is blocked by a barrier of glass temporarily placed there by the
experimenter, and the only way of escape to the nest-box is an indirect
route by way of _B_ and the white box. Ordinarily the shock was given only
when the mouse entered the wrong box, not when it retreated from it; it
was never given when the right box was chosen. The box to be chosen,
whether it was white, gray, or black, will be called the right box. The
electric shock served as a means of forcing the animal to use its
discriminating ability. But the question of motives in the tests is not so
simple as might appear from this statement.
The reader will wonder why the mouse should have any tendency to enter
_B_, and why after so doing, it should trouble to go further, knowing, as
it does from previous experiences, that entering one of the electric-boxes
may result in discomfort. The fact is, a dancer has no very constant
tendency to go from _A_ to _B_ at the beginning of the tests, but after it
has become accustomed to the box and has learned what the situation
demands, it shows eagerness to make the trip from _A_ to _B_, and thence
by way of either the right or the left route to _A_. That the mouse should
be willing to enter either of the electric-boxes, after it has experienced
the shock, is even more surprising than its eagerness to run from _A_ to
_B_. When first tested for brightness discrimination in this apparatus, a
dancer usually hesitated at the entrance to the electric-boxes, and this
hesitation increased rapidly unless it were able to discriminate the boxes
by their difference in brightness and thus to choose the right one. During
the period of increasing hesitancy in making the choice, the experimenter,
by carefully moving from _I_ toward the entrances to the electric-boxes a
piece of cardboard which extended all the way across _B_, greatly
increased the mouse's desire to enter one of the boxes by depriving it of
dancing space in _B_. If an individual which did not know which entrance
to choose were permitted to run about in _B_, it would often do so for
minutes at a time without approaching the entrance to the boxes; but the
same individual, when confined to a dancing space 4 or 5 cm. wide in front
of the entrances, would enter one of the electric-boxes almost
immediately. This facilitation of choice by decrease in the amount of
space for whirling was not to any considerable extent the result of fear,
for all the dancers experimented with were tame, and instead of forcing
them to rush into one of the boxes blindly and without attempt at
discrimination, the narrowing of the space simply increased their efforts
to discriminate. The common mouse when subjected to similar experimental
conditions is likely to be frightened by being forced to approach the
entrances to the boxes, and fails to choose; it rushes into one box
directly, and in consequence it is as often wrong as right. The dancer
always chooses, but its eagerness to choose is markedly increased by the
restriction of its movements to a narrow space in front of the entrances
between which it is required to discriminate. It is evident that the
animal is uncomfortable in a space which is too narrow for it to whirl in
freely. It must have room to dance. This furnished a sufficiently strong
motive for the entering of the electric-boxes. It must avoid disagreeable
and unfavorable stimuli. This is a basis for attempts to choose, by visual
discrimination, the electric-box in which the shock is not given. It may
safely be said that the success of the majority of the experiments of this
book depended upon three facts: (1) the dancer's tendency to avoid
disagreeable external conditions, (2) its escape-from-confinement-
impelling need of space in which to dance freely, and (3) its abundant and
incessant activity.
Of these three conditions of success in the experiments, the second and
third made possible the advantageous use of the first. For the avoidance
of a disagreeable stimulus could be made use of effectively in the tests
just because the mice are so restless and so active. In fact their
eagerness to do things is so great that the experimenter, instead of
having to wait for them to perform the desired act, often is forced to
make them wait while he completes his observation and record. In this
respect they are unlike most other animals.
My experiments with the dancer differ from those which have been made by
most students of mammalian behavior in one important respect. I have used
punishment instead of reward as the chief motive for the proper
performance of the required act. Usually in experiments with mammals
hunger has been the motive depended upon. The animals have been required
to follow a certain devious path, to escape from a box by working a
button, a bolt, a lever, or to gain entrance to a box by the use of teeth,
claws, hands, or body weight and thus obtain food as a reward. There are
two very serious objections to the use of the desire for food as a motive
in animal behavior experiments--objections which in my opinion render it
almost worthless in the case of many mammals. These are the discomfort of
the animal and the impossibility of keeping the motive even fairly
constant. However prevalent the experience of starvation may be in the
life of an animal, it is not pleasant to think of subjecting it to extreme
hunger in the laboratory for the sake of finding out what it can do to
obtain food. Satisfactory results can be obtained in an experiment whose
success depends chiefly upon hunger only when the animal is so hungry that
it constantly does its best to obtain food, and when the desire for food
is equally strong and equally effective as a spur to action in the
repetitions of the experiment day after day. It is easy enough to get
almost any mammal into a condition of utter hunger, but it is practically
impossible to have the desire for food of the same strength day after day.
In short, the desire for food is unsatisfactory as a motive in animal
behavior work, first, because a condition of utter hunger, as has been
demonstrated with certain mammals, is unfavorable for the performance of
complex acts, second, because it is impossible to control the strength of
the motive, and finally, because it is an inhumane method of
experimentation.
In general, the method of punishment is more satisfactory than the method
of reward, because it can be controlled to a greater extent. The
experimenter cannot force his subject to desire food; he can, however,
force it to discriminate between conditions to the best of its knowledge
and ability by giving it a disagreeable stimulus every time it makes a
mistake. In other words, the conditions upon which the avoidance of a
disagreeable factor in the environment depends are far simpler and much
more constant than those upon which the seeking of an agreeable factor
depends. Situations which are potentially beneficial to the animal attract
it in varying degrees according to its internal condition; situations
which are potentially disagreeable or injurious repel it with a constancy
which is remarkable. The favorable stimulus solicits a positive response;
the unfavorable stimulus demands a negative response.
Finally, in connection with the discussion of motives, it is an important
fact that forms of reward are far harder to find than forms of punishment.
Many animals feed only at long intervals, are inactive, do not try to
escape from confinement, cannot be induced to seek a particular spot, in a
word, do not react positively to any of the situations or conditions which
are employed usually in behavior experiments. It is, however, almost
always possible to find some disagreeable stimulus which such an animal
will attempt to avoid.
As it happens, the dancer is an animal which does not stand the lack of
food well enough to make hunger a possible motive. I was driven to make
use of the avoiding reaction, and it has proved so satisfactory that I am
now using it widely in connection with experiments on other animals. The
use of the induction shock, upon which I depended almost wholly in the
discrimination experiments with the dancer, requires care; but I am
confident that no reasonable objection to the conduct of the experiments
could be made on the ground of cruelty, for the strength of the current
was carefully regulated and the shocks were given only for an instant at
intervals. The best proof of the humaneness of the method is the fact that
the animals continued in perfect health during months of experimentation.
The brightness discrimination tests demanded, in addition to motives for
choice, adequate precautions against discrimination by other than visual
factors, and, for that matter, by other visual factors than that of
brightness. The mouse might choose, for example, not the white or the
black box, but the box which was to the right or to the left, in
accordance with its experience in the previous test. This would be
discrimination by position. As a matter of fact, the animals have a strong
tendency at first to go uniformly either to the right or to the left
entrance. This tendency will be exhibited in the results of the tests.
Again, discrimination might depend upon the odors of the cardboards or
upon slight differences in their shape, texture, or position. Before
conclusive evidence of brightness discrimination could be obtained, all of
these and other possibilities of discrimination had to be eliminated by
check tests. I shall describe the various precautions taken in the
experiments to guard against errors in interpretation, in order to show
the lengths to which an experimenter may be driven in his search for
safely interpretable results.
To exclude choice by position, the cardboards were moved from one
electric-box to the other. When the change was made regularly, so that
white was alternately on the right and the left, the mouse soon learned to
go alternately to the right box and the left without stopping to notice
the visual factor. This was prevented by changing the position of the
cardboards irregularly.
Discrimination by the odor, texture, shape, and position of the cardboards
was excluded by the use of different kinds of cardboards, by changing the
form and position of them in check tests, and by coating them with
shellac.
The brightness vision tests described in this chapter were made in a room
which is lighted from the south only, with the experiment box directed
away from the windows. The light from the windows shone upon the
cardboards at the entrances to the electric-boxes, not into the eyes of
the mouse as it approached them. Each mouse used in the experiments was
given a series of ten tests in succession daily. The experiment was
conducted as follows. A dancer was placed in _A_, where it usually ran
about restlessly until it happened to find its way into _B_. Having
discovered that the swing door at _I_ could be pushed open, the animal
seemed to take satisfaction in passing through into _B_ as soon as it had
been placed in or had returned to _A_. In _B_, choice of two entrances,
one of which was brighter than the other, was forced by the animal's need
of space for free movement. If the right box happened to be chosen, the
mouse returned to _A_ and was ready for another test; if it entered the
wrong box, the electric shock was given, and it was compelled to retreat
from the box and enter the other one instead. In the early tests with an
individual, a series sometimes covered from twenty to thirty minutes; in
later tests, provided the condition of discrimination was favorable, it
did not occupy more than ten minutes.
To exhibit the methods of keeping the records of these experiments and
certain features of the results, two sample record sheets are reproduced
below. The first of these sheets, Table 6, represents the results given by
No. 5, a female,[1] in her first series of white-black tests. Table 7
presents the results of the eleventh series of tests given to the same
individual.
[Footnote 1: It is to be remembered that the even numbers always designate
males; the odd numbers, females.]
In the descriptions of the various visual experiments of this and the
following chapters, the first word of the couplet which describes the
condition of the experiment, for example, white-black, always designates
the visual condition which the animal was to choose, the second that which
it was to avoid on penalty of an electric shock. In the case of Tables 6
and 7, for example, white cardboard was placed in one box, black in the
other, and the animal was required to enter the white box. In the tables
the first column at the left gives the number of the test, the second the
positions of the cardboards, and the third and fourth the result of the
choice. The first test of Table 6 was made with the white cardboard on the
box which stood at the left of the mouse as it approached from _A_, and,
consequently, with the black cardboard on the right. As is indicated by
the record in the "wrong" column, the mouse chose the black instead of the
white. The result of this first series was choice of the white box four
times as compared with choice of the black box six times. On the eleventh
day, that is, after No. 5 had been given 100 tests in this brightness
vision experiment, she made no mistakes in a series of ten trials (Table
7).
TABLE 6
BRIGHTNESS DISCRIMINATION
White-Black, Series 1
Experimented on No. 5 January 15, 1906
POSITION OF
TEST CARDBOARDS RIGHT WRONG
1 White left -- Wrong
2 White right -- Wrong
3 White left -- Wrong
4 White right -- Wrong
5 White left Right --
6 White right Right --
7 White left -- Wrong
8 White right Right
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