828 NUTRITION AND HEAT REGULATION. 



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. 



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 582 

 calories. 



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. 



*See Rubner, " Zeitschrift. f. Biologie," 19, 535, 1883; and Richet, " La 

 chaleur animale," 1889, p. 224. 



