154 



THE HUMAN MOTOR 



Thus, taking water at t' = 20, q' = 598 small calories per 

 gramme of water. 



The total heat of vaporisation is thus measured. 



Regnault gave a more complete formula, which would give, in 

 this case, 595 calories, Atwater and Rosa adopted 592 small 

 calories or 0-592 great calories (*), for the cooling of vapour from 

 37 to 20. 



The quantity of heat carried away in water vapour represents 

 between 20 and 25% of the total expenditure. Thus in the 

 above example : 



881 x 0-592 -521-55 Cal. 



From the whole of their experiments, on men from 22 to 34 

 years old, the American professors concluded that the losses 

 specified above amount to from 25% to 75% of the energy 

 dissipated by radiation and convection from the surface of the 

 body when the temperature of the surrounding atmosphere was 

 20C. 



An error is introduced if the temperature of the subject varies, 

 if entering at 36-7C, for instance, he came out of the calorimeter 

 at 37-7 C. In this case rise of 1C corresponds to an absorption 

 by the body of 0-83 Cal. X 65 = 54 Calories, the specific heat 

 of the human body ( a ) being 0-83 and the weight of the subject 

 65 kilogrammes. There will be a loss of 54 calories in the case of 

 a similar fall of temperature. But, in repose, the temperature 

 varies very little, and is usually the same at leaving as in entering 

 the chamber. In any case, the temperature was noted every 

 four minutes by means of an electrical thermometer placed in the 

 " rectum." Temperatures could be read to T o of a degree ( 3 ) 

 by the deflections of the galvanometer. 



The daily variations of the rectal temperature of a man in re- 

 pose and well fed, are shown on the chart (fig. 133). 



37.05 



37.3 



3V 



36.9 



36,7 



36.5 



36.3 



2* 



0123456769 W U 12 13 W 1516&- M 19 2021 22 ^3'2t 



Fw. 133. 



Curve of the temperature of male subject during 24 hours. 



(M Atwater and Rosa (Bulletin, No. 63, p. 59, 1899). 



( 2 ) Pembrey : Schaefer's Textbook of Physiol'., i., p.' 839, 1898. Rosen- 

 thai (Archiv. f. Physiol., 1875). 



( 8 ) Benedict and Snell (PflUger's Archiv., vol. Ixxxviii., p. 492 ; ex., 33, 

 1901-2) . 



