860 NUTRITION AND HEAT REGULATION. 



Outgo | 



Income : Potential energy of material metabolized in body = 5459 Cal. 

 Energy given off from the body as heat .... 4833 Cal. 

 Heat equivalent of muscular work 602 Cal. 



5435 Cal. 5435 Cal. 



Experimental error 24 Cal. 



Results of Calorimetric Measurements. The actual results 

 obtained from direct calorimetric measurements corroborate those 

 deduced from the study of the energy given off in the oxidation of 

 the foodstuffs of the daily diet. They show that man gives off heat 

 from his body to the amount of 40,000 to 50,000 calories per kgm. 

 of weight during 24 hours under conditions of ordinary life, a 

 total, therefore, of 2,400,000 to 3,000,000 calories per day for an 

 individual weighing 60 kgms. This amount is increased greatly 

 under conditions demanding much muscular work. This loss of 

 heat is, of course, made good by the production of an equal amount 

 within the body by the oxidation of the food material. Actual 

 experiments upon different animals* show that small animals 

 produce more heat in proportion to their weight than larger animals 

 of the same species, owing to their relatively larger surface and 

 therefore greater loss of heat. Birds produce and lose more heat 

 for a unit of surface than mammals, a fact which indicates that 

 their physiological oxidations are more intense. According to 

 Richet, a sparrow gives off per unit of surface five times as much 

 heat as a rabbit. According to Rubner, the sparrow produces 

 thirteen times as much heat as man for the same amount of tissue. 

 In infants, owing to their larger surface relative to the mass of the 

 body, the loss of heat is greater than in the adult. 



HEAT REGULATION. 



From a general standpoint the most important problem that the 

 physiologist has to study 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 controlling the loss of heat as well as the produc- 

 tion of heat, and under the conditions 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. 



*See Eubner, " Zeitschrift. f. Biologic," 19, 535, 1883; and Richet, "La 

 chaleur animate," 1889, p. 224. 



