242 ANIMAL HEAT. 



is the quantity of blood which, is exposed to the cooling 

 influence of the air diminished or increased, so far as is 

 known, in accordance with any need in relation to tempe- 

 rature. 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 some extent, to vary also. But the 

 respiratory passages, while they must be considered important 

 means by which heat is lost, are altogether subordinate in 

 the power of regulating the temperature, to the skin. 



It may seem to have been assumed, in the foregoing 

 pages, that the only regulating apparatus for temperature 

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

 produce a cooling effect ; and as if the amount of heat pro- 

 duced were always, therefore, in excess of that which is 

 required. Such an assumption would be incorrect. We 

 have the power of regulating the production of heat, as 

 well as its loss. 



In food we have a means for elevating our temperature. 

 It is the fuel, indeed, on which animal heat ultimately 

 depends altogether. Thus, when more heat is wanted, we 

 instinctively take more food, and take such kinds of it as 

 are good for combustion ; while everyday experience shows 

 the different power of resisting cold possessed by the well- 

 fed and by the starved. 



In northern regions, again, and in the colder seasons of 

 more southern climes, the quantity of food consumed is 

 (speaking very generally) greater than that consumed by 

 the same men or animals in opposite conditions of climate 

 and seasons. And the food which appears naturally 

 adapted to the inhabitants of the coldest climates, such as 

 the several fatty and oily substances, abounds in carbon 

 and hydrogen, and is fitted to combine with the large 

 quantities of oxygen which, breathing cold dense air, they 

 absorb from their lungs. 



In exercise, again, we have an important means of 

 raising the temperature of our bodies (p. 233). 



