RELATION OF FOOD TO WORK, AND 279 



actually sufficient to produce tlie meclianical force necessary to maintain 

 the muscular exertion of walkiug 20 or 21 miles per day. 



1. The urea excreted bears to the proteine consumed the proportion 

 of 24 to 79, as api)ears from their chemical compositions, viz : 



Urea C2 H4 X2 O2 ...... 60 



Proteine C36 H27 X4 On 395 



2. In 100 parts of proteine there are 53.7 parts of carbon, and 7 parts 

 of hydrogen ; the total heat due to the combustion of 1 gram of pro- 

 teine is, therefore. 



Heat-units. 



0. 537 gram of carbon 4. 3389 



0. 070 gram of hydrogen 2. 4123 



6. 7512 



This number, 6.7512, represents the maximum quantity of heat-units* 

 that could be produced by the combustion of 1 gram of proteine ; but 

 the term depending on hydrogen in it should be reduced to five-ninths 

 of its amount, in consequence of the hydrogen already combined with 

 oxygen in the proteine. Hence we find — 



Combustion of one gram of inoteine. 



Heat-units. 



Carbon 4. 3389 



Hydrogen 1. 3402 



5. 6791 



3. In 100 parts of urea there are 20 parts of carbon, and 6| parts of 

 hydrogen ; the total heat, therefore, due to the combustion of 1 gram 

 of urea is : 



Heat-units. 



0. 20 gram of carbon 1. 6160 



0. 067 gram of hydrogen 2. 3089 



3. 9249 



The term depending on hydrogen, in this result, should be reduced 

 to one-half, in consequence of the hydrogen already combined with oxygen 

 in the urea. 



Hence we find — 



Combustion of one gram of urea. 



Heat-units. 



Carbon 1. 6160 



Hydrogen , 1. 1544 



2. 7704 



* Heat-unit = 1 kilogram of water raised 1- C. 



