RESULTS OF CALORIMETRIC MEASUREMENTS. 967 



They have devised a simple formula for estimating the surface 

 area in terms of the height and weight of the individual. 



A = W<>-425 x HO-725 x 71.84 



Making use of this formula, whose average error is about 

 1.7 per cent., they find that in adult] life the basal metabol- 

 ism of different individuals shows a quite constant relationship 

 to the surface area. As stated above, the average figure indi- 

 cates a heat production of 40 Calories per hour per square 

 meter of surface. With advancing age there is a slight falling 

 off in metabolism, while in infancy and childhood there is a 

 notable increase. The relationship as pictured by these observ- 

 ers is illustrated in the accompanying chart (Fig. 3016). 



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 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 



It is obvious that the relative importance of these factors will vary 



