BODY TEMPERATURE OF MICE 345 



In the course of endeavoring to rear young mice in the cold 

 room used in my experiments, it was often found that the mother 

 threw the young out of the nest and allowed them to die. This I 

 explained on the supposition that the mice became so cold, during 

 the absence of the mother from the nest, that they occasioned 

 her discomfort upon her return, and were on that account re- 

 jected. The truth of this belief was strengthened by the fact 

 that such young mice at first felt unpleasantly cold to the hand, 

 but they could quickly be warmed to body temperature, and were 

 then accepted by the mother. During the earlier days of their life, 

 the young could endure more severe and more prolonged exposure 

 to cold than later. For example, I have recorded that four mice, 

 only a day old, were left at a maximum temperature of 13.5°C. 

 (probably much colder part of the time) for a period of ten to 

 twelve hours, during which time their body temperature was 

 undoubtedly not far above that of the air. When warmed up, 

 these young mice were accepted by the mother and lived for four 

 days thereafter. 



In the course of the present series of exper'ments, exactly 100 

 temperature tests were made upon young mice, varying in age 

 from less than one day to twenty-one days. The number of 

 individuals used was only slightly less than this, since the process 

 of taking the temperature almost invariably involved the killing 

 of the animal. 



On the whole, the results derived from this series of experiments 

 are to be regarded as more satisfactory than those derived from 

 the experiments with adults. This is partly for the reason that 

 the temperature changes undergone by the young in consequence 

 of atmospheric changes are as a rule very much more pronounced 

 than in the case of adults; partly for the reason that the young, 

 at least in the earlier stages, are not affected by the excitement 

 and struggle by which the older animals are affected. Likewise 

 the available number of comparable figures is greater for the 

 former. 



With the exception of the first four mice tested, thermometer 

 'number 3' (p. 320) was employed in these experiments, owing to 



