570 THE ANIMAL BODY AS A MACHINE 



Cals. 

 Proteins: 



Casein . . . ......... .... r . . 5.86 



Egg-albumin 5.74 



Serum-albumin 5.92 



Average 5.84 



Fats: 



Tissue-fat . 9 . 48 



Butter-fat - 9.23 



Olive oil 9.33 



Average 9.35 



Carbohydrates : 



Glucose 3.74 



Cane-sugar 3.96 



Milk-sugar . 3.95 



Maltose 3.95 



Starch 4.18 



Average 3.96 



The figures usually employed for the fats and carbohydrates as 

 they actually occur in a mixed diet are those which were originally 

 estimated by Rubner, namely: 



One gram of fat = 9.3 calories 



One gram of carbohydrate = 4.1 calories 



the high value for carbohydrates being employed on account of the 

 predominance of starch among the carbohydrates of an ordinary 

 mixed diet. 



The heat-value of carbohydrates and fats for the body must be the 

 same as that indicated by the combustion-calorimeter, since the 

 products of combustion are in both cases identical, namely, carbon 

 dioxide and water. The case is far different for the Proteins, however, 

 because these are not completely burnt, the nitrogen being excreted 

 in the form of urea, creatinine and so forth, which are substances still 

 capable of yielding heat when they are completely oxidized. Further- 

 more, the proteins as they actually occur in the diet are not com- 

 pletely digested and assimilated, a proportion of indigestible or diffi- 

 cultly assimilable material being evacuated in the feces. The true 

 heat-value of protein to the animal body is therefore not indicated by 

 the combustion-calorimeter. 



The determination of the actual calorific value of protein in the 

 animal body was first carried out by Rubner. His procedure was as 

 follows: The calorific value of dried muscle-tissue was determined 

 in the combustion-calorimeter, and the heat- values of the urine and 

 feces upon an exclusive meat-diet were also determined. Subtract- 

 ing the heat-value of the excreta from that of the food, and also a 

 small correction representing the heat of solution of the urea in the 

 urine, it was found that an average of about 4.1 calories per gram 

 was actually available to. the animal from the protein in its diet. The 



