BODY TEMPERATURE OF MICE 353 



in air temperature. Less certain (owing to scarcity of data) is 

 the conclusion that, after such a reduction, the mice tended to 

 recover their normal temperature, even while the external cold 

 persisted. 



7. The mean figure obtained by averaging the warm-room and 

 cold-room averages, for both males and females, is 36.66°C. This 

 is based upon 54 readings, comprizing only those which are not 

 believed to have been affected by abnormal conditions. 



8. Two mice in these experiments lost their power of heat 

 regulation, and displayed subnormal temperatures, the body tem- 

 perature of one falling to about 12.5°C. 



For very young mice (from less than one day to twenty-one 

 days), the following conclusions may be offered, based upon 100 

 tests : 



1. Very young mice, when exposed to a cold atmosphere, soon 

 assume body temperatures very much lower than those which 

 are normal for adult animals. In no case, however, did the body 

 temperature, in my own experiments, fall nearly to that of the 

 air, the lowest figure recorded being about 15.5°C., which resulted 

 from the exposure of a twelve-day mouse for thirty minutes to 

 an atmospheric temperature of 6°. Since the period of exposure, 

 in these experiments, never exceeded one and one-half hours, it 

 is not at all likely that my figures represent the limit to which 

 the body temperature of young mice may fall without fatal 

 results. 



2. The power of heat regulation, for moderate air temperatures 

 (20° to 25°), is pretty well established at about the age of ten 

 days. For lower temperatures, however, the power of regulation 

 is not developed until much later, apparently not until the age 

 of twenty days, under the conditions of my own experiments. 

 Three mice, eighteen daj^s old, exposed for thirty to sixty minutes 

 to an atmosphere of about 7°C., reached a mean body tempera- 

 ture of 23.3°, or 13° lower than that of mice of the same age kept 

 in the warm room. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 15, NO. 3 



