1094 ANIMAL HEAT 



thermal animals, the terms of cold-blooded and warm-blooded are not 

 well chosen. This classification, therefore, rests upon their power of 

 retaining a relatively constant body-temperature. 



It should be noted especially that the temperature of the poikilo- 

 thermal animals is invariably somewhat higher than that of the 

 medium in which they live. This discrepancy cannot surprise us, 

 because even an apparently perfectly inactive animal cannot suppress 

 its metabolism entirely, and hence, since it must generate at least a 

 slight amount of heat, its temperature must remain at least a degree 

 or two above that of the surrounding medium. In other words, 

 even cold-blooded animals store their heat in a certain measure, but 

 this storage is never considerable, because they are relatively unpro- 

 tected against heat-loss and secondly, because their metabolism per 

 unit of weight is much lower than that of the warm-blooded animals. It 

 should also be noted that the temperature of the warm-blooded animals 

 is not absolutely uniform, because those leading a more active life, 

 possess a higher body-temperature than those which do not. This 

 becomes apparent immediately if the rectal temperature of the birds 

 (41 to 44 C.) is compared with that of the mouse (41 C.), rabbit 

 (39 C.), dog (38 to 39 C.), man (37 C.), and horse (36 C. to 37 C.). 1 

 With the exception of a few hibernating animals, which are homoiother- 

 mic in summer and poikilothermic in winter, the temperature of the 

 warm-blooded animals must remain rather constant, otherwise certain 

 conditions may arise which will make life impossible. 2 The vitality of 

 cold-blooded animals, on the other hand, is not seriously impaired by 

 such variations, as is evinced by the fact that the temperature of 

 the frog may be reduced from 25 C. to 5 C. without producing other 

 symptoms than a mere sluggishness of movement. 



The Temperature of Different Regions of the Body. It has been 

 stated above that the different tissues of our body eliminate heat in 

 amounts corresponding almost precisely with the intensity of their 

 metabolism. The muscles come first, then the glands, and lastly the 

 nervous and connective tissues. Furthermore, while the heat pro- 

 duced by them is directly transmitted from part to part, the chief and 

 final absorbing medium is the blood, but since the latter cannot equalize 

 conditions instantaneously, some internal parts must always be 

 warmer than others. This is true, in particular, of the liver, because 

 its blood-vessels are well protected against heat loss, and because 

 its metabolism is never at a standstill. But, the blood also trav- 

 erses certain regions which lie in immediate contact with the medium 

 and which, therefore, are more directly exposed to the influence of the 

 latter. Thus, it has been observed that the temperature of the skin 

 in the vicinity of a blood-vessel is higher than that at some distance 

 from it, and that the temperature of the blood of the carotid artery is 



1 Frothingham and Minot, Am. Jour, of Physiol., xxx, 1912, 430. 



2 Simpson, Proc. R. Soc. (Edinb.) 1912, and Proc. Soc. Exp. Biol. and Med., 

 1913. 



