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The Dancing Mouse

R >> Robert M. Yerkes >> The Dancing Mouse




[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.

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