THE MAINTENANCE OF THE ANIMAL HEAT. 377 



VARIATIONS IN TEMPERATURE. 



The temperature of warm-blooded animals is not abso- 

 lutely constant by any means. Thus, mammals which go 

 into a winter sleep, hibernate, as we say, have their tem- 

 perature sink several degrees, in this way approaching some- 

 what the cold-blooded animals. The advantage of being 

 able to lie in this protracted sleep at a somewhat reduced 

 bodily temperature is, of course, very evident when we re- 

 member the saving of tissue on this account. Some of the 

 mammals show a transition to the lower classes in their 

 temperature. Thus, the temperature of the monotremes, a 

 group of animals to which the Duck-bill belongs, is nor- 

 mally no higher than 30 C. 



There are also differences in the temperatures of differ- 

 ent classes of warm-blooded animals. Thus, as a rule, the 

 temperature of larger animals is less than that of smaller 

 ones. In the case of birds the highest temperature is 

 reached, running up as high as from 40 to 45 C. This 

 in the human body would be a fever-heat and would in all 

 probability prove fatal. This relatively much higher tem- 

 perature in birds no doubt facilitates muscular contraction, 

 and may be easily explained by relating it to the flight of 

 birds. 



But differences in temperature may occur in the same 

 individual. Thus, there are differences on account of age. 

 The temperature of an infant is usually the highest, being 

 about 37 9 /io C. From this it sinks to about 37Vio, which 

 is the temperature of active adult life. As age advances 

 the temperature sinks still further, and at seventy is about 

 36 8 /io. However, in real old age it begins to rise again 

 and frequently reaches 37 4 /io, almost the temperature of an 

 infant. Numerous observations seem to show, too, that 

 the temperature in females is slightly lower than in males. 



There are even differences in temperature in the differ- 

 ent regions of the same body, the highest temperature be- 

 ing reached in the liver and the internal glands, where it 

 is not infrequently and normally from 38 to 39 C. The 



