960 



NUTRITION AND HEAT REGULATION. 



may be increased or decreased. In exophthalmic goiter, for ex- 

 ample, it may be increased as much as 75 per cent. (Du Bois). 



yeaw . 



Fig. 301d. — The curves represent the suggested total daily calories according to age, the 

 solid line the curve for boys, the broken line for girls. The dots represent the calories taken in 

 individual observations on boys, the circles those taken on girls. (From Holt and Fales, 

 loc. cit.) 



HEAT REGULATION. 



From a general standpoint the most important problem that the 

 physiologist has to study in regard to animal heat is the means 

 by which the heat production and heat loss are so regulated as to 

 maintain a practically constant body temperature. Experiments 

 show that the mechanism of heat regulation is very complex and 

 is two-sided — that is, the body possesses means of controlHng the 

 loss of heat as well as the production of heat, and under the con- 

 ditions of normal life both means are used. 



Regulation of the Heat Loss. — Heat is regularly lost from our 

 bodies in a number of different ways, which may be classified as 

 follows : 



1. Through the excreta, urine, feces, saliva, which are at the temperature 



of the body when voided. 



2. Through the expired air. This air is warmer than the inspired air, 



and, moreover, is nearly saturated with water-vapor. The vaporiza- 

 tion of water requires heat, which is, of course, taken from the body 

 supply. Each gram of water requires for its vaporization about 0.5 cal. 



3. By evaporation of the sweat from the skin. The amount lost in this 



way increases naturally with the amount of sweat secreted. 



4. By conduction and especially by radiation of heat from the skin. 



The relative values of these different means of heat loss are 

 estimated as follows by Vierordt: 



1. By urine and feces 1.8 per cent, or 48 calories. 



2. By expired air: Warming of air 3.5 " " 84 



Vaporization of water from lungs 7.2 " " 182 



3. By evaporation from skin 14.5 " " 364 



4. By radiation and conduction from skin 73.0 " " 1792 



Total daily loss = 2470 



