The Dancing Mouse
REVIEWS AND CRITICISM.
The Animal Behavior Series, Vol. 1. :Author: Robert M. Yerkes. The Macmillan Company, 1907. Pp. xxi-{-290. In this book the author not only presents the results of his own investigations on the dancing mouse, but he also tries to give as complete an account of this animal as possible on the basis of the literature. The dancing mouse has received this name for its curious capacity in the execution of quick, graceful, bizarre and oft-repeated movements, which are somewhat similar to our way of dancing. These mice are frequently kept as pets and they are, as the author says, inexhaustible sources of amusement as well as invaluable material for studies in animal behavior and intelligence. The dancer did not make its appearance as an object of scientific study before 1890. Naturally considerable interest was taken in the origin of this race, because the animals by their peculiar movements are unfit for the usual conditions of mouse-existence, so that they are thrown on human care. It can not be definitely settled when and where the race originated; very likely it is several centuries old.
The dancers are imported from Japan, where they are known as Chinese mice. From this one may conclude that the race originated in China, although nothing definite could be settled by historical research. The variation is now firmly established and breeds true to its type, so that one cannot call it pathological, although there is evidence that dancers appear sometimes among common mice.
After some remarks on the feeding, breeding and development of the animals, the author proceeds to give the results of his study of the dancing movements. It is curious to note that the previous investigators disagree in their descriptions of the movements of the dancer, although this is the most striking feature of the behavior of these animals. By observing the movements of a large number of animals at regular hours of the day the author found that the activity of the dancer increases steadily from the morning to the evening, when it reaches its maximum, and there exist large individual differences as to the execution of the dancing movements. There are three kinds of dancers: those which whirl almost uniformly to the right, those which whirl to the left, and those which whirl almost as frequently in one direction as in the other. It seems that there might be some sex differences in this respect, the males being more frequently left whirlers, whereas the females seem to be more frequently right whirlers; the evidence, however, is not conclusive. The author remarks justly at the end of this chapter, that one of the most interesting results of his study of the movements of the dancer is the fact that in even so simple a matter the truth cannot be discovered except by long and careful observation, and that the method of getting knowledge of the (183) behavior of animals by impressions, verified by a few observations, is worse than valueless.
Chapters IY and Y contain a study of equilibration and dizziness in the dancer and of the relation of these phenomena to structural facts. Besides the dancing movements the following peculiarities of the dancer demand an explanation in terms of structural facts: restlessness, and quick jerky movements of the head; lack of responsiveness to sounds; greater or less deficiency in equilibration and orientational power; lack of visual dizziness and lack of rotational dizziness. It seems very natural to refer these facts to structural peculiarities of those portions of the body which are-supposed to control movements and to be the cause of the phenomena of dizziness and of the ability to perceive sounds, i. c., to some deviation from the type of the mammalian ear in the structure of the semicircular canals and of the cochlea. A considerable amount of time has been spent to establish a significant difference of these organs of the dancers from those of the common mice. The discussion of the results obtained by Rawitz, Panse, Baginski, Alexander and Kreidl, and by Kishi, shows that no structural peculiarity was discovered which accounts satisfactorily for the behavior of the dancers. There is no doubt that the peculiarities of the behavior are caused by some structural differences, but it is certain that they cannot be accounted for by differences in the sense organs alone, and it seems to be doubtful whether they can be accounted for in terms of the structure of the peripheral and of the central nervous system. The author comes to the conclusion that the structure of the entire organism will have to be taken into account. The next chapter gives the author’s own investigations on the sense of hearing of the dancers. The results of previous investigations seem to have shown almost without exception that the dancers lack the sense of hearing. Those experiments, in which reactions of the dancer to sound stimuli were observed, are open to criticism in so far as the possibility that the mice did not react to other stimuli was not excluded. A close study of the animals shows that the adult dancer is totally deaf, but the young dancer perceives sounds for a few days of the third week of his life. Shortly before this period the young dancer becomes very excitable and pugnacious.
Chapters YII-XI are devoted to the study of the sense of sight of the dancer. These chapters cover 108 pages, or almost one-half of the book, and they contain exclusively the results of the author’s experiments; references to the literature are given only when it is necessary to define the relation of the author’s results and conclusions to those of previous investigators. The results refer to brightness vision, to color vision and to the role of sight in the daily life of the dancer. The labyrinth method was used with the greatest advantage. The dancer’s tendency to avoid disagreeable external conditions, its need of space to dance freely and its abundant activity make this animal extremely fit for study by laboratory methods. The author expresses the view that the dancer may take the same part in comparative psyREVIEWS AND CRITICISM. 185 chology as the frog in physiology. The labyrinth method as used by the author differs in one respect from all previous experiments with the labyrinth, in so far as punishment instead of reward was used as the chief motive for the proper performance of the required act. The punishment applied was a slight induction shock. This method is not only less cruel, because it avoids subjecting the animals to extreme hunger, but it is also more effective, because a hungry animal is in a state of discomfort and it is impossible to keep the conditions even fairly constant. The results of the experiments on vision show that the dancer possesses the ability to discriminate brightness differences of reflected light as well as of transmitted light, but that it has not a color sense like ours. The animal probably discriminates colors of the red end of the spectrum from those of other regions by differences in the stimulating value of light of different wave lengths, red having a very low stimulating value; the stimulating effect of different wave lengths for the dancing mouse, is radically different from that of different wave lengths for the human eye. The retina of the dancer is reported to contain only one type of retinal element, but no details 011 this point are given. The role of the sense of sight in the life of the dancer is not very great; movement and differences in brightness are the only visual conditions which to any considerable extent control the activity of this animal.
The rest of the book deals with the question of how the dancer may profit by experience, and with problems which are related to this question. It contains interesting remarks about the different methods of training and about their efficiency. One chapter gives some observations on the question of relearning; an acquired habit it lost only gradually, and even after a very long interval the process of relearning requires less time than the original acquirement of the habit. Chapter XVII describes some observations on individual, age and sex differences; this investigation is not completed because in the course of the experiments almost all the animals were lost by disease. The last chapter contains some remarks about the inheritance of forms of behavior; the author comes to the conclusion that there is no evidence of an inheritance of acquired habits.
For the student of human psychology two parts of the book are of special interest: the chapter where the author discusses the results of the anatomical observations 011 the ear of the dancer, and the one where he describes his “Weber’s law experiments.” The observations 011 the peculiarities of the dancer were put to a very interesting use by Cyon, who used them as a basis for his theory of space. This physiologist remarked several difficulties in the definitions of space, among them the difficulty of finding a reason why we conceive space as three-dimensional. Cyon gives the answer that the source of this difficulty is the fact that space is a sense quality and therefore indefinable, just in the same way as blue or red is indefinable. He then proceeds to find the organ of this sixth sense, and chiefly 011 the basis of some observations 011 the abnormal structure of the ear of the dancer he comes to the conclusion that the semicircular canals are the organ of this sense, and that we conceive space as three-dimensional, because the three dimensions of space correspond to the three canals. Since the appearance of Yerkes’ book another article of Cyon has come out in which the author continues the building up of his theory, and one may expect the publication of a full account of his theory in the near future. Many of those who are interested in the theory of space have not an opportunity to follow the development of physiological and anatomical questions, and Yerkes’ excellent account will be very welcome to them. Cyon’s theory is very ingenious, and for this reason it is important not to forget that it rests only on a meagre empirical basis.
The chapter on Weber’s law is probably the least satisfactory in the book. In these experiments the mice were trained to recognize a box which was distinguished from another only by a different intensity of light. The smallest difference of intensity where an effect of the training could be observed was taken for the just perceptible difference. The difficulty consists in defining what an effect of training is. The results of the experiments are given in figures which show how many times a certain event occurred in a total number of cases. The question arises when do these numbers indicate an effect of training? This question, by its very nature, cannot be answered definitely without laying down an arbitrary limit, because the numbers of relative frequency would show some variation also if the experiments were repeated under exactly the same conditions. It is doubtful whether the question as to the applicability of Weber’s law for animals can be answered at present, and it does not seem that the author materially advances the problem by his results, chiefly because of the lack of an adequate definition of a just perceptible difference for experiments with animals. The sober attitude of not asking a question which cannot be answered by our present means would seem to be in better agreement with the general spirit of this excellent book.
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