Part 6 (1/2)
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; Kis.h.i.+ 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 Kis.h.i.+ 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 Kis.h.i.+, 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 j.a.panese 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 a.n.a.logous 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 Kis.h.i.+.
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 Kis.h.i.+, gives evidence of accuracy and trustworthiness. The fact that the statements of Alexander and Kreidl frequently do not agree with those of Kis.h.i.+ 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 s.p.a.ce 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 ca.n.a.ls 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 a.s.suming 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 mult.i.tudinous 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, Kis.h.i.+, 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 Konig 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 repet.i.tion 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 s.e.x, 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 s.e.xual 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 gla.s.s 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 a.s.serting that my mice, young (12-13 days) as well as old, do not react to the Konig Galton whistle (7210 Vs.). They could not be awakened out of sleep by repet.i.tions 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 Kis.h.i.+ (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, Kis.h.i.+, 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 s.e.xually 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 Konig tuning forks which gave tones varying in pitch from 1024 to 16,382 complete vibrations.