412 



VITAL HEAT. 



90,000 calories or 90 ktlogramdeyrees i. 6., for each degree of 

 increase in the temperature of the apparatus 90 kilogramdegrees 

 are absorbed. 



Besides the heat which is absorbed by the calorimeter, addi- 

 tional amounts are given off by the subject of the experiment in 

 its expired air, and expended in evaporation of the water from its 

 lungs and skin. To ascertain these, the amount of air supplied 

 and its temperature on entering and leaving the instrument must 

 be determined, also the amount of water in the air. 



Air calorimeters are also used, such as that of Haldane, Hale 

 White, and Washbourn (Fig. 230). In this instrument the animal 

 is placed in the chamber C, and hydrogen is burnt in H. The 

 tubes A A and A' A' being closed, the heat dissipated by the 

 animal expands the air in the air-space between the walls of the 

 chamber, and increases the pressure on that side of the fluid in 

 the manometer M, causing it to move toward H. The flame of 

 hydrogen is regulated so that the amount of heat which is pro- 

 duced by its combustion counterbalances that of the animal and 

 keeps the fluid in the manometer stationary. From the amount of 

 water produced the amount of hydrogen burnt is calculated, and 



FIG. 230. Diagram of air calorimeter : F, layer of felt ; A, tubes for ventilation - r 

 V, cage; H, hydrogen flame ; M, manometer (Haldane, Hale White, and Washbourn). 



the number of calories produced by its burning is determined, 

 which equals that given off from the animal. 



Although there are produced in the adult human body between 

 2000 and 3000 kilocalories of heat daily (p. 409), still this is very 

 materially affected by various conditions. Thus, children produce 

 proportionately more than adults ; strong, than weak persons ; 

 fleshy persons, than those who are thin. 



Diet is another very important factor, as shown by the follow- 

 ing table (Danilewsky), giving the amount of heat produced under 

 different diets : 



On a minimum diet 1800 kilogramdegrees. 



On a reduced diet (absolute rest) .... 1989 



On a non-nitrogenous diet 2480 



On a mixed diet (moderate work) .... 3210 



On an abundant diet (hard work) .... 3646 



On an abundant diet (very laborious work) 3780 



