The Dancing Mouse by Robert M. Yerkes

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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 fuer 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 fuer 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 cooeperation 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.

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