NOKMAL PROCESSES OF ENEKGY METABOLISM 549 



only for the formation of water, Boussingault(fc) sought to establish the 

 exact amount of hydrogen burned by striking an exact and complete 

 balance of materials between the ingesta and the ejecta of the body. 



The heat of combustion of carbon and hydrogen having already been 

 established at 8.040 and 34.46 kilo-calories per gram respectively, Helm- 

 holtz calculated by Dulong's method that a man of 82 kg., giving off in 

 the respiration in 24 hours 878.4 gm. CO 2 or 239.6 gm. C produced 

 (239.6 X 8.04 =) 1,925 calories. The excess of oxygen going to form 

 water combined with 13.615 gm. H producing (13.615 X 34.46 =) 

 469.172 calories. The total heat production therefore was 2395.55 Cal. 



Vierordt by a method entirely analogous to that of Boussingault cal- 

 culated the heat production from the known metabolism of food as fol- 

 lows: Taking the average ration of the adult at 120 gm. protein, 90 gm. 

 fat and 340 gm. carbohydrate and leaving out of account the hydrogen 

 of the carbohydrate, because it was known to be saturated with oxygen, 

 there were in 



O -Ll! 



120 gm. protein 64.18 8.60 



90 " fat 70.32 10.26 



340 " carbohydrate 146.80 



Total 281.20 18.86 



But the urine and feces contained unoxidized carbon and hydrogen de- 

 termined at 29.8 gm. for the former and 6.3 gm. for the latter. The net 

 combustion, therefore, was (281.20 29.8 =) 251.4 gm. C and (18.86 

 6.3 =) 12.56 gm. H, and the heat production 



251.4 X 8.04 = 2031.31 Cal. 

 12.56 X 34.36 = 332.82 " 



Total 2364.13 " 



These methods of calculating the heat production upon the heats of 

 combustion of hydrogen and carbon contained in the food as if the hydro- 

 gen and carbon were free gases are now known to contain an error of at 

 least 11 or 12 per cent. The heat of combustion of formic acid (CO 2 H 2 ), 

 for example, is not equal to the combustion heat value of C and H 2 5 for 

 the heat value of H 2 is 683 Cal. per gram-mol and of C is 943 Cal. per 

 gram-mol; whereas that of CO 2 H 2 is only 694 Cal. per gram-mol. The 

 difference between the combustion heat value of CO 2 H 2 and the sum of 

 the values for C and H 2 is called the heat of formation. 



The heat production, therefore, must be based upon the combustion 

 of the organic foodstuffs themselves. 



2. Calculation from the Heats of Combustion of the Organic Food- 

 stuffs. Berthelot and Andre determined the physiological heat value 

 of protein (egg albumin coagulated and dried at 100 C.) by burning in 



