HEAT-BALANCE. 



399 



linen, silk, leather, oil-cloth. (6) Clothing that is in direct contact with the skin 

 naturally also takes up the excrementitious products of the skin, linen and cotton 

 in greatest amount, and wool least of all transmitting the waste matters to the 

 overlying clothing. The drawers take up the least material, the shirt twice as 

 much, the socks eight times as much. 



The temperature of the surface of the body beneath winter-clothing is on the 

 average 18 C. and beneath summer-clothing 20 C. Heat is given off principally 

 by conduction when clothing is worn. Clothing appears comfortable when the 

 temperature of its surface is 5 or 6 C. higher than that of the air. 



HEAT-BALANCE. 



As the temperature of the body is capable of remaining constant 

 within narrow limits, it is obvious that the amount of heat taken up 

 must be equivalent to the amount of heat given off, that is exactly so 

 much potential energy must within a given time be converted into heat 

 as heat is given off from the body. Attempts have been made from 

 different points of view to set up heat-balances which while partly at 

 least without a reliable foundation, are nevertheless of great inter- 

 est in the elucidation of the heat-economy of the animal organism. 

 An adult produces on an average enough heat to raise the temperature 

 of his body almost i C. in half an hour. If no heat were given off, the 

 body would in a short time become enormously heated in thirty-six 

 hours to the boiling-point providing the production of heat continued 

 uninterruptedly . 



HEAT-BALANCE ACCORDING TO H. v. HELMHOLTZ. 



Hermann von Helmholtz was the first, in 1846, to determine numerically the 

 amount of heat produced by man. 



1. Heat-income. (a) A healthy adult, weighing 82 kilos, 

 expires in twenty-four hours 878.4 grams of carbon dioxid. 

 The combustion of the carbon thereof into carbon dioxid 



generates 1,730,760 calories 



(6) The man, however, takes up more oxygen than is 

 present in the carbon dioxid given off. This excess is em- 

 ployed for purposes of oxidation, particularly for the forma- 

 tion of water through the combustion of hydrogen. In conse- 

 quence of the excess of oxygen thus taken up 13,615 grams 

 of hydrogen can be additionally burned up, yielding 318,600 



2,049,360 calories 



(c) About 25 per cent, of heat must be derived from 

 other sources than combustion-processes, so that in round 



figures there will be . 2,732,000 calories 



This amount would in fact suffice to raise the temperature of a human body 

 weighing from 88 to 90 kilos from an average temperature of 10, 28 or 29C., 

 thus to 38 or 39 C., that is the normal temperature. 



2. Heat-expenditure. According to v. Helmholtz the following debits must be 

 set against the heat-income : 



(a) For the heating of food and drink, 

 which have an average temperature of 1 2 C . . . 7 - J 5 7 calories = 2 . 6 per cent . 



(6) For heating the inspired air = 16,400 

 grams, assuming the temperature of the air to 

 be 20 C r 70,032 =2.6 per cent. 



[If the temperature of the air were o the 

 number of calories would be 140,064 = 5.2 

 per cent.] 



(c} 656 grams of water evaporated through 

 the lungs 397-536 = 14.7 per cent. 



(d) The remainder through radiation and 



evaporation from the external integument . . . from 77.5 per cent, to 80. i percent. 



