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The Dancing Mouse

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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.

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