Decreased Pressure 1003 



but making reservations ~ 7 about the exactness of the values which 

 we are obliged to use; at least they give us an approximation. 



Let us suppose that a man weighing 60 kilograms produces in 24 

 hours 2800 kilogram calories, 18 and let us consider first the expendi- 

 ture of heat which he would need to maintain at the normal level 

 (on the average, 38°) the mass of his body in an air whose tem- 

 perature is 19°. 



If we assume that this man admits to his lungs in 24 hours 12 

 kiloliters of air, whose temperature will be raised from 19°, we 

 shall find, since the calorific capacity of the air is 0.26, that there 

 will have been expended thus in calories 12 X 19 X 0.26 = 59.28 

 calories. The pulmonary evaporation of 500 grams of water (prob- 

 ably a maximum quantity) will necessitate a loss of 292 calories 

 (the heat of vaporization being 0.582) . 



The heating of drink and food, the excretion of urine and the 

 faeces causes a loss of heat which Helmholtz estimates at 2.6% of 

 the total loss, here some 65 calories. 



Here then is a known expenditure, which I admit is necessary, 

 of 59 -f- 292 + 65 = 416 calories. There remain about 2500 calories 

 lost; 1, by cutaneous radiation and the contact with the air; 2, by 

 cutaneous evaporation: this is on the average estimated at 1 kilo- 

 liter, consuming thus 582 calories. Are these losses justified, in the 

 circumstances in which we are placed, by the physical necessities of 

 maintaining at the temperature of 38° a body weighing 60 kilo- 

 grams, having about 13,000 sq. cm. of surface, with a caloric capacity 

 about equal to that of water, and surrounded by air at 19°? That is 

 what I should like to be able to settle here. Unfortunately, scien- 

 tific data at present do not permit us to settle this problem, 29 and 

 we should have to undertake special researches on this point. 



A priori, I cannot help believing that it is needless to lose by 

 simple cutaneous evaporation a kilogram of water per day, and 

 consequently 582 calories; this expenditure can be justified only by 

 an excess of heat produced, which radiation and contact cannot 

 throw off. How can we understand that heat is produced with the 

 sole purpose of losing it afterwards? This excess appears much 

 greater when we consider the human body producing work; the 

 unutilized heat becomes so great that an abundant sweat must 

 remove it by evaporation. Now it may very well be that mountain 

 dwellers have a better regulated machine, which, instead of de- 

 voting to work only 18% to 20% of the force expended, is con- 

 siderably more efficient, and consequently, for the same dynamic 

 expenditure, requires a smaller absorption of oxygen and of food 



