THE ENERGY EQUATION. 397 



it may be ignored for the present purpose. We have then the 

 following deductions to make: 



Potential energy in 80 gm. of fat stored 752,000 



133 gm. of feces '. 180,000 



1,424 gm. of urine 110,000 



1,042,000 



This leaves as a balance to be calculated as kinetic energy 



3,728,200 

 1,042,000 



2,686,200 calories 



Another method of calculation deals with the carbon and hydrogen of the 

 food and feces only. The heat production was at one time assumed to de- 

 pend on the combustion of the carbon of the fats, carbohydrates and pro- 

 teins and the hydrogen of the fats and proteins. The hydrogen of the car- 

 bohydrates was not considered because it was supposed to be closely com- 

 bined with the oxygen present in the same compounds in such a form as 

 to yield no more heat on oxidation. In like manner the combustion heats 

 of the urine and feces may be calculated from the whole carbon and hydro- 

 gen content of the organic substances. The total carbon of the food in the 

 experiment is 395 gm., of the hydrogen in fats and proteins 23.8 gm. The 

 carbon of the urine and feces is 24.9 gm., while the hydrogen of the urine 

 and feces is about 5.2 gm. We have then: 



Heat units from 359 gm. of food carbon 2,907,900 



Heat units from 23.8 gm. of food hydrogen 813,900 



3,721,800 3J2l,8oo 



Heat units from 24.9 gm. of excreta carbon 201,690 



Heat units from 5.2 gm. of excreta hydrogen 177,840 



379,530 379,530 



Net calories 3,342,270 



From this result the value of the energy stored as fat would have to be 

 subtracted as before. This method of calculation gives a somewhat lower 

 result than the other, and largely because of the uncertainty in allowing 

 for the excreted carbon and hydrogen, but it has value as a comparison 

 process. 



Respiration Calorimeters. In experiments with men or large animals on 

 the combustion of food and liberation of heat some kind of respiration ap- 

 paratus is employed. Some modification of a type originally introduced 

 by Pettenkofer is generally used. In this the subject is placed in a cham- 

 ber with double walls through which a current of air may be forced and 



