NORMAL PKOCESSES OF ENERGY METABOLISM 555 



was first applied by Rubner to the results obtained by Voit and Petten- 

 koft'er on a fasting nuiri ( Lusk(/i) ). These observers had found that their 

 subject, weighing 71.01) kgm., gave off in the respiration and in the urine 

 207.11 gm. carbon and in the urine 11.33 gm. nitrogen. Deducting from 

 the total carbon the carbon (3.28 times the N) belonging to protein the re- 

 mainder was calculated as carbon of fat and it was learned that the man had 

 burned 70.81 gin. protein and 22.1 gm. fat. Rubner applied his physio- 

 logical heat values for a gram of N in starvation (24.98 Cal.) and for a 

 gram of carbon in fat (12.3 Cal.) and learned that the total energy pro- 

 duction of the man in twenty-four hours was: 



11.33 gm. 1ST x 2498 = 283 Cal. 



166.95 gm. C of fat x 12.3 = 2091 Cal. 



Total 2374 Cal. 



When the food contains only fat and protein exactly the same method 

 is used for calculating the heat production, except that the heat value of 

 nitrogen in the urine has a different value (see page 552). When the 

 food contains carbohydrate any gain or loss of C to the body may be esti- 

 mated as fat, it being assumed that the amount of glycogen in the tissues 

 is the same at the end of an experiment as at the beginning. It will be 

 seen later that Rubner, employing this method of calculation in experi- 

 ments on the dogs whose heat production was measured simultaneously in 

 a calorimeter, found perfect agreement between the heat as calculated and 

 as measured, thereby proving the essential correctness of the method. At- 

 water's method of calculation in similar experiments on human subjects 

 was different, but proved to be equally correct. 



3. The Method of Thermal Quotients of 2 and C0 2 . When an or- 

 ganic foodstuff is burned in the animal body a definite amount of oxygen 

 is absorbed and a definite amount of CO 2 is formed and eliminated. If. the 

 heat formed by such a combustion is known the heat value of a gram 

 of oxygen absorbed or of a gram of CO 2 eliminated may be expressed as 

 a simple quotient of heat divided by the weight of the gas. Since the 

 measurement of the respiratory gases by volume is an easy matter the 

 thermal quotient can be expressed also in relation to a liter of gas at C. 

 and 760 mm. of pressure or at any other desired temperature. 



a. Calculation of Thermal Quotients. If we suppose that protein 

 burns only to the stage of urea the thermal quotient for this foodstuff 

 may be calculated from the following equation : 



C 72 H 112 1S T 18 SO 22 + 77 O 2 63 C0 2 + 37 H 2 O + 9 COX 2 H 4 + H 2 S0 4 

 Albumin Urea 



According to this equation 1.612 gm. of protein yielding 7.810 Cal. of heat 

 would consume 77 molecules of O 2 weighing (77 X 32 ==) 2.464 gm. and 



