322 HANDBOOK OF PHYSIOLOGY. 



(b.) Loss of Heat from the Lungs. As a means for lowering the tem- 

 perature, the lungs and air-passages are very inferior to the skin ; al- 

 though, by giving heat to the air we breathe, they stand next to the 

 skin in importance. As a regulating power, the inferiority is still more 

 marked. The air which is expelled from the lungs leaves the body at 

 about the temperature of the blood, and is always saturated with moist- 

 ure. No inverse proportion, therefore, exists, as in the case of the skin, 

 between the loss of heat by radiation and conduction on the one hand, 

 and by evaporation on the other. The colder the air, for example, the 

 greater will be the loss in all ways. Neither is the quantity of blood 

 which is exposed to the cooling influence of the air diminished or in- 

 creased, 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 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. 



(c.) By Clothing. The influence of external coverings for the body 

 must not be unnoticed. In warm-blooded animals, they are always 

 adapted, among other purposes, to the maintenance of uniform temper- 

 ature ; and man adapts for himself such as are, for the same purpose, 

 fitted to the various climates to which he is exposed. By their means, 

 and by his command over food and fire, he maintains his temperature on 

 all accessible parts of the surface of the earth. 



II. Methods of Variation in the Amount of Heat Produced. 

 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 produced 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. 



(a.) By Regulating the Quantity and Quality of the Food taken. 

 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 every-day experience 

 shows the different power of resisting cold possessed, respectively, 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 season. And the food 

 which appears naturally adapted to the inhabitants of the coldest cli- 

 mates, such as the several fatty and oily substances, abounds in carbon 

 and hydrogen, and is fitted to combine ultimately with the large quanti- 



