VARIATION IN THE PRODUCTION OF HEAT 437 



the air diminished or increased in the lungs, so far as is known, in accordance 

 with any need in relation to temperature. It is true that by varying the 

 number and depth of the respirations, the quantity of heat given off by the 

 lungs may be made to vary also for a few minutes. But the respiratory 

 passages, while they must be considered important means by which heat is 

 lost, are altogether subordinate, in the power of actively regulating the tem- 

 perature. 



The loss of heat used to warm foods is an obvious method of expenditure 

 of heat which may be resorted to, especially in certain fevers. The loss of 

 heat by the excreta discharged from the body at a high temperature must be 

 of little use as a means of regulating the temperature, since the amount so 

 lost must be capable of little variation. 



Variation in the Production of Heat. It may seem to have been 

 assumed, in the foregoing pages, that the only regulating apparatus for tem- 

 perature required by the human body is one that shall, more or less, produce 

 a cooling effect; as if the amount of heat produced were always, there- 

 fore, in excess of that which is required. Such an assumption would be in- 

 correct. The body has the power of regulating the production of heat, as 

 well as its loss. 



The production of heat in the body is apparently different for each ani- 

 mal; i.e., the absolute amount of heat set free by different animals in a given 

 period varies. Each individual has his own coefficient of heat production. 

 From all that has been said on the subject it will be seen that the amount of 

 heat for all practical purposes depends upon the metabolism of the tissues of 

 the body ; everything, therefore, which increases that metabolism will increase 

 the heat production; so, therefore, the absolute amount of heat produced by a 

 large animal, having a larger amount of tissues in which metabolism may 

 go on, will be, c&teris paribus, greater than that of a small animal. But the 

 activity of the tissue change in a small animal may be greater than in a large 

 one, as measured per kilo of body-weight, and naturally no strict line can be 

 drawn between the two. 



HEAT PRODUCED PER KILO PER HOUR. (MUNK.) 



Man 1.5 calories 



Dog (large) 1.7 



Dog (small) 3.8 



Guinea-pig 7.5 



Rat 11.3 



Mouse 19.0 



Sparrow 35.5 



The ingestion of foods increases the metabolism of the tissues. As one 

 would expect, the rate of heat production is found by experiment upon the 

 dog to be increased after a meal, reaching its height about six hours after 

 a meal. 



