THE TEMPERATURE OF THE BODY 405 



than mammals, and the temperature of small warm-blooded animals 

 is in most cases higher than that of large ones. This can be seen 

 from the following table : 



Hedgehog 34-8-3o-5 C. Man, rectum . . 37-2 (98-96 F.) 



Dog .. 37-5-39-5 C. axilla .. 36-9 (98-45 F.) 



Rabbit .. 38-3-39-9 C. mouth .. 36-87 (98-36 F.) 



Guinea-pig 37-3-39-5 C. Infants . . . . 37-6 



Pigeon . . 41-0-42-5 C. 



The lower vertebrata, such as reptiles, fish, amphibia, are cold- 

 blooded that is to say, they maintain their body temperature scarcely 

 above that of the surrounding air or water. Fish may be frozen, and 

 recover if carefully thawed. A frog in winter becomes cooled down, 

 and hibernates; in summer it is warmed up, and becomes active. 

 The mammal, by maintaining a uniform body temperature, is active 

 in all the seasons. A hibernating mammal changes from warm- to 

 cold-blooded when food becomes scarce in the winter. A hibernating 

 animal will not allow itself to be frozen. It wakes up, and in a short 

 while becomes warm-blooded. 



In between these two classes warm- and cold-blooded come the 

 rarer egg-laying marsupials of Australia, such as Echidna and Ornitho- 

 rhynchus. The power of these animals to regulate their body tempera- 

 ture at a constant level is less well developed than in mammals, but 

 their temperature in a _cold atmosphere is always many degrees 

 above the surrounding medium. For example, the normal tempera- 

 ture of Echidna is 



At 4 0. 25-5 C. 



At 20 C . . . . 28-6 C. 



At 30 C 30-9 C. 



At 35 C 34-8 C. 



The Regulation of the Body Temperature depends upon nervous 

 control. In young birds just before hatching, and in prematurely born 

 mammals, this mechanism is not working, they have to be kept warm. 

 A child born at the seventh month has to be carefully wrapped in 

 cotton-wool, or even placed in an incubator. At birth at full time, 

 on the other hand, the heat-regulating mechanism is working in man, 

 and for this reason so much care need not be taken to prevent heat 

 loss. Some mammals, such as the rabbit, which is born naked, do 

 not acquire the power of regulation until a considerable time after 

 birth. The newly-born guinea-pig, on the other hand, is born covered 

 with hair, and can regulate its temperature. The newly hatched 

 chick can regulate its temperature: the naked young of many birds, 

 on the other hand, are not able to do so. 



The evidence as to the existence of a centre regulating the 

 temperature of the body is conflicting. It is known that lesions 

 of the central nervous system in certain regions e.g., the optic 

 thalamus and corpus striatum, pons, and medulla produce an upset 

 of the power of heat regulation, but it would not be exact to describe 

 any one of these sites as the " heat-regulating centre " of the body. 



