496 APPLIED BIOLOGY 



calorimeter could not be burned in an animal body. F.ur 

 example, a gram of pure carbon (charcoal) gives 8.08 calories, 

 and a gram of hydrogen would give 34.5 calories ; but neither 

 of these could be oxidized at the temperature suitable : * 

 protoplasm. This shows the importance of determin 

 whether foods give as much heat in an animal body as ir 

 calorimeter ; and this hs 3 been tested with a special ap 

 ratus as follows : 



419. Calorimeter for Living Animals. This consists 

 a small room with walls arranged to prevent heat conductk/' 

 as far as possible, with coils of metallic pipes arranged so that 

 circulating water will absorb heat from the air in the room, 

 and with machinery for ventilation. Delicate apparatus 

 attached to the pipes for supplying air and water recor^ 1 

 changes in temperature, and chemical analyses are made '? 

 foods, breathed air, and excretions. There is also inside t 1 - 

 room a foot-power machine connected with a small dynarru 

 or otherwise arranged so that the man may treadle thej 

 machine and thus do easy, moderate, or hard work for eight 

 hours per day. Thus it is possible to determine the effect 

 of different amounts of work upon food requirements. 



Inside such a special calorimeter men have often lived 

 constantly for several days at a time ; and chemists have 

 carefully compared the heat value of the foods oxidized 

 with the heat given off from their bodies to the air of the room 

 and measured by the apparatus. 



The results of many such experiments have shown that 

 foods are oxidized as stated in 418 above. The apparatus 

 has proved of great value in cases where the value of a food 

 to a living animal or to man was unknown. For example, 

 the dispute as to whether alcohol is a food ( 472) has been 

 settled by showing that in very small quantities alcohol 

 serves as a food for energy ; and that the amount so usable 

 is so small as to be of no interest in the ordinary daily diet 

 of healthy persons. 



