ANIMAL HEAT AND FEVER. 135 



haves more or less like a cold-blooded animal for some time im- 

 mediately following birth, during which period it must there- 

 fore be carefully protected from cooling, for, if its temperature 

 be allowed to fall to any considerable extent, it is not likely to 

 survive. It takes several months before the heat regulating 

 mechanism becomes so developed that the infant can withstand 

 any considerable degree of cold. 



Factors Concerned in Maintaining the Body Temperature. 

 The body temperature is a balance between heat production and 

 heat loss. Heat is produced by combustion of the organic food- 

 stuffs in the muscles, the amount which each foodstuff thus pro- 

 duces being the same as when it is burned outside the body, 

 except in the case of protein, where allowance must be made for 

 the incomplete combustion of this substance in the animal body 

 (see p. 85). The muscles are therefore the furnaces of the ani- 

 mal body, the fuel being the organic foodstuffs. Heat is lost 

 from the body mainly from the skin, but partly also from the 

 lungs and in excreta. Heat loss from the skin is brought about 

 by the utilization of several physical processes, namely: (1) by 

 conduction along objects which are in contact with the skin or 

 through the air; (2) by convection, that is, by being carried 

 away in currents of air which move about the body ; (3) by radi- 

 ation; (4) by evaporation of sweat. This last is the means by 

 which most heat can be lost, because it takes a large amount of 

 latent heat to vaporize the sweat (see p. 20). 



Heat loss from the lungs is mainly due to vaporization of 

 water, with which the expired air is saturated. A small amount 

 is also absorbed in warming the air itself. The heat lost in the 

 urine and fasces is almost negligible. 



The Regulation of the Body Temperature. It is plain that 

 a very sensitive regulatory mechanism must exist in order that 

 the production and loss of heat may be so adjusted as to keep the 

 body temperature practically constant. When heat loss becomes 

 excessive, then must heat production be increased to maintain the 

 balance, and vice versa when heat loss is slight. The conditions 

 are to a certain extent comparable with those obtaining in a 

 house heated by a furnace and radiators and provided with a 



