594 JOHN R. MURLIN 



Calories 



(1) Warming food and drink to body temperature 42 



(2) Warming air from 17.5 to 30 C 35 



(3) Evaporation of water from lungs and skin 558 



(4) Heat equivalent of external work done 51 



(5) Loss of radiation from entire surface of body 1,181 



(6) Loss by conduction to air from entire surface 833 



Total , 2,700 



Atwater, in his calorimetric studies, made the following estimations: 



I. Resting man, mean of fourteen experiments comprising forty-two days: 



Calories 



1. Heat loss by radiation and conduction 1,683 



2. Heat loss by urine and feces 31 



3. Heat loss by evaporation from lungs and skin 548 



Total 2,262 



H. Man at work, mean of twenty experiments comprising sixty-six days: 



Calories 



1. Heat loss by radiation and conduction 3,340 



2. Heat loss by urine and feces 46 



3. Heat loss by evaporation from lungs 'and skin 859 



4. Heat equivalent of -muscular work 451 



total 4,676 



It is evident, from these estimates, that fully eighty per cent of all the 

 heat produced in the body is lost through the skin. 



2. The Law of Surface Area. Closely related to this matter of the 

 loss of heat through the skin is the relationship of heat loss to heat pro- 

 duction known as the law of surface area, first enunciated over 80 years 

 ago by certain French writers. To quote one of the earliest communica- 

 tions: "As the heat loss is proportional to the extent of free surfaces and 

 these latter are to each other as the squares of their homologous sides, it 

 follows of necessity that the quantity of oxygen absorbed, or what amounts 

 to the same thing, the heat produced on the one hand and lost on the other, 

 is proportional to the square of the corresponding dimensions of the ani- 

 mals one is comparing (Robiquet and Thillaye)." The first experimental 

 evidence of relationship between skin surface and the food requirement of 

 animals seems to have been furnished by Miintz who in 1879 investigated 

 the maintenance ration of horses. Emphasizing the part played by the sur- 

 face he says : "A notable part of the food certainly is consumed to main- 

 tain the vital heat which has a tendency constantly to be lost by radiation 

 or conduction to the surrounding medium. Another cause of cooling is 

 cutaneous evaporation which is a function of the surface if it is not directly 

 proportional thereto. The evaporation produced by the organs of respira- 

 tion may equally be regarded as having a relation to the surface of the body 

 rather than to the weight. We are then by these considerations in position 





