[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.
[Footnote 1: A cereal food.]
Success in keeping and breeding dancing mice depends upon three things: cleanliness, warmth, and food supply. The temperature should be fairly constant, between 60° and 70° Fahr. They cannot stand exposure to cold or lack of food. If one obtains good healthy, fertile individuals, keeps them in perfectly clean cages with soft nesting materials, maintains a temperature of not far above or below 65°, and regularly supplies them with pure water and food which they like, there is not likely to be trouble either in keeping or breeding these delicate little creatures. Several persons who have reported to me difficulty in rearing the young or in keeping the adults for long periods have been unable to maintain a sufficiently high or constant temperature, or have given them food which caused intestinal trouble.
The males are likely to fight if kept together, and they may even kill one another. A male may be kept with one or more females, or several females may be kept together, for the females rarely, in my experience, fight, and the males seldom harm the females. Unless the male is removed from the cage in which the female is kept before the young are born, he is likely to kill the newborn animals. When a female is seen to be building a nest in preparation for a litter, it is best to place her in a cage by herself so that she may not be disturbed.