THE EXTERNAL ENVIRONMENT 243 



178. Influence of Water and of Baths. The circumstances in 

 which a man works immersed in water are rare. In swimmers 

 the calorific expenditure is modified by the force of the current 

 and the temperature of the water ; the resistance to be overcome 



R = K x S X V 2 . 



K may be taken as 73 and S as -034 square metres, (*) Hence if 

 the velocity of the current is 4 metres we have : 



R 73 x 0-035 X 16 = 41 kilogrammes. 



If the water is calm, only the chemical and thermic actions need 

 be considered ; the former intervene by phenomena known of 

 osmotic exchanges between the salts of the organism and the 

 water especially when the latter itself is salt. The thermic 

 actions are more appreciable. Jules Lefevre made a thorough 

 study of them : a subject was immersed in a mass of water, M, 

 contained in a bath ; and the temperature was raised by 6 in t 

 minutes. The specific heat of water being unity, the hourly 

 expenditure : 



Lefevre established that the calorific production varies inversely 

 with that of the temperature of the bath. The thermic expendi- 

 ture per minute would be given approximately by the following 

 formula : q = 22-556 Cal. 0-843 t 0-0178~/ 2 + 0-00124 t* 

 0-OOOOltt*. 



This is true between + 5 and +34 C. ; 



The expenditure per minute was : 



Temperature ...... +5 12 18 24 30C 



?perminute ......... 18-05 11-7 7-2 4 2 Calories. 



Lefevre's law, as fig. 145 shows, would lead to a calorific pro- 

 duction of 1,200 calories in 24 hours for a temperature of 35. By 

 experiment he obtained a value of 1,500 Calories, on the average, 

 both by the preceding method and by the expenditure of 

 oxygen. ( 2 ) The physiological energy was therefore estimated, 

 by him, to be 1,500 calories, instead of 900 calories, which is the 

 largest value which the writer can accept. ( 3 ) 



The influence of water, like that of the air, is relatively greater 

 on short subjects than on tall, because it is a surface action. 



(*) Other authorities take K = 55, which lowers the value of the resist- 

 ance R. Also note that S is the surface of the biggest section of the 

 immersed body, and that R is expressed in kilogrammes). 



( 2 ) Jules Lefevre (loc. cit., pp. 907, 908) and for the action of baths (pp. 417- 

 422). See also 252. 



(3) The value, 1/500 Cal. is even greater than the total calorific expenditure 

 during sleep ( 104). 



