Effects of External Conditions 113 
modifications, and the number of measurements applied to the 
animals was considerably increased. 
Temperature. ‘The mean temperature” of the warm room for 
the entire season was 26.30° C. (79.34° F.), that for the cold room 
6.16° C. (43.08° F.). These figures correspond roughly to those 
for the mean annual temperatures of Key West or Porto Rico, on 
the one hand, and those for Eastport, Maine, or Minneapolis, 
Minn., on the other.2® But it would not, of course, be at all fair 
to compare the temperature conditions of the experimental rooms 
with those of the points named, still less to compare the climatic 
conditions as a whole. 
The mean daily range of temperature (1. e., mean difference 
between the maximum and minimum for each day) was 11.9? C. 
(21.4° F.)-in the warm room, 6.7° C. (12° F.) in the cold room. 
The maximum temperature reached at any time in the warm room 
was about 40° C. (for very brief periods), the minimum in the cold 
room being — 14.4°. But these figures represent exceptional occur- 
rences and have little significance. Curves have been con- 
structed (Fig. 1) showing the mean daily temperature in each room 
during the entire period of the experiment. 
It is plain, of course, that none of these figures can represent 
the actual temperatures to which the mice themselves were most 
of the time exposed. When huddled together in large numbers 
in a nest of cotton-waste, the temperature of the air immediately 
in contact with them, at least in the case of the cold-room animals, 
was doubtless very much higher than that in the room outside, 
i. e., that recorded by the thermograph. Nevertheless, we all 
know by experience the difference between sleeping in a cold 
room and sleeping in a warm one, even when the amount of bed- 
ding is varied to suit the circumstances. And it must be remem- 
bered that during part of the time the mice were feeding, exploring 
the cages, etc., and were then wholly exposed to the air. 
Humidity. The relative humidity in the warm room (see p. 100 
above) ranged from about 22 per cent to about 66 per cent, the 
” The mean temperatures here given are based upon four figures daily, these being taken from the 
thermograph sheets. 
20 Report U. S. Weather Bureau for 1906-1907. 
