ANIMAL HEAT. 315 



Although under any ordinary circumstances, the external application 

 of cold only temporarily depresses the temperature to a slight extent, it 

 is otherwise in cases of high temperature in fever. In these cases a tepid 

 bath may reduce the temperature several degrees, and the effect so pro- 

 duced lasts in some cases for many hours. 



(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; although, 

 by giving heat to the air we breathe, they stand next to the skin in im- 

 portance. 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 moisture. No 

 inverse proportion, therefore, exists 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 increased, so far as is known, in accordance with 

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

 ber 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 temper- 

 ature, 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 tempera- 

 ture; 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 

 ojily 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. 



(,) 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 



