550 JOHN K MURLIN 



the calorimeter and deducting the quantity of heat represented by the 

 urea formed from it. The bomb value of the protein was 5.600 calories 

 and the urea 833, leaving a net value to the organism of 4.857 calories per 

 gram. The average values for eleven different food proteins was found 

 by them to be 5.691 Cal. and the net value after deducting the urea formed 

 was 4.750 Cal. per gram. 



In the conclusion to their paper Berthelot and Andre state that the 

 influence of the intestinal excretions "cannot modify these figures very 

 much for the f eces in man form a very small fraction of the weight of the 

 food." The unabsorbed residue from proteins it is now known, however, 

 constitute as much as 10 to 15 per cent of the food; hence they are by no 

 means negligible. 



The exact physiological heat values of these organic foodstuffs was 

 first resolved with a high degree of exactness by Rubuer(fJ). He proceeded 

 from the known fact that in the case of proteins, urea is not the only nitro- 

 genous waste product and that some of the others have very different heat 

 values from that of urea. Besides he saw the necessity of deducting the 

 heat value of the feces resulting from the food in question. An example 

 of the method employed by Rubner may T)e given as follows: 



Lean meat free of connective tissue was taken and dried; it was then 

 macerated in alcohol to insure its complete dehydration. After drying 

 again and evaporation of the alcohol it was macerated once more in ether. 

 The albumin resulting had the appearance of papier mache and was prac- 

 tically free of salts. When this material was powdered and burned a 

 bomb heat value of 5.754 Cal. per gram was obtained. 



A dog was fed for eight days with 116.8 grams of the dried and puri- 

 fied protein daily. The urine for the first six days was rejected, and that 

 for the 7th and 8th days only saved, the dried residue of which gave 

 a heat value of 2.706 calories per gram. The heat value of urea he found 

 to be only 2.523 Cal. or 7 per cent less than that of the whole urine. One 

 gram of the dried matter was found to contain 0.414 gm. of N, from which 

 it was found that 1 grn. of N" in the urine represented 6.690 calories. 



The feces contained 37,8 gm. of dry matter daily. The loss by non- 

 absorption therefore was 3.24 per cent. Burned in the calorimeter this 

 dry matter was found to contain 5.722 calories per gram. When the ash 

 was deducted it was found to have a heat value per gram of 6.852 calorics, 

 and the nitrogen was found to be 7.02 per cent. The net physiological 

 neat value therefore could be calculated as follows : 



Ingested 100 gm. dry protein of meat 575.40 Cal. 



-P fUriiic 109.450 Cal. 



Excreta^ 



Feces 18.540 



Total -- approx. 128.000 



Difference 447.400 or 4.47 Cal. per gram. 



