CALORIFIC VALUE OF THE FOODSTUFFS. 829 



exercised an extraordinarily fruitful influence upon the entire study 

 of metabolism and nutrition, and this is due in great measure to the work 

 of RUBNER. 



This energy of the various foods may be represented by the amount 

 of heat which is set free in their combustion. This quantity of heat is 

 expressed as calories, and a small calorie is the quantity of heat necessary 

 to warm 1 gram of water from to 1 C. A large calorie is the quantity 

 of heat necessary to warm 1 kilo of water 1 C. Here and in the follow- 

 ing pages large calories are to be understood. There are numerous 

 investigations by different experimenters, such as FRANKLAND, DAN- 

 ILFWSKI, RUBNER, BERTHELOT, STOHMANN, BENEDICT and OSBORNE, 

 and others, on the calorific value of different foodstuffs. The following 

 results, which represent the calorific value of a few nutritive bodies on 

 complete combustion outside of the body to the highest oxidation prod- 

 ucts, are taken from STOHMANN'S l work. 



Calories. 



Casein 5 . 86 



Ovalbumin 5 . 74 



Conglutin 5 .48 



Protein (average) 5.71 



Animal tissue-fat 9 . 50 



Butter-fat 9.23 



Cane-sugar 3 . 96 



Milk-sugar 3 . 95 



Dextrose 3 . 74 



Starch 4.19 



Fats and carbohydrates are completely burnt in the body, and one can 

 therefore consider their combustion equivalent as a measure of the living 

 force developed by them within the organism. We generally designate 

 9.3 and 4.1 calories for each gram of substance as the average for the 

 physiological calorific value of fats and carbohydrates respectively. 



The proteins act differently from the fats and carbohydrates. They 

 are only incompletely burnt, and they yield certain decomposition prod- 

 ucts, which, leaving the body with the excreta, still represent a certain 

 quantity of energy which is lost to the body. The heat of combustion 

 of the proteins is smaller within the crganism than outside of it, and they 

 must therefore be specially determined. For this purpose RUBNER 2 

 fed a dog on washed meat, and he subtracted from the heat of combustion 

 of the food the heat of combustion of the urine and feces, which corre- 

 sponded to the food taken plus the quantity of heat necessary for the 

 swelling up of the proteins and the solution of the urea. RUBNER has 

 also tried to determine the heat of combustion of the proteins (muscle- 



1 See Rubner, Zeitschr. f . Biologie, 21, which also cites the works of Frankland and 

 Danilewski; see also Berthelot, Compt. rend., 102, 104, and 110; Stohmann, Zeitschr. 

 f. Biologie, 31; Benedict and Osborne (vegetable proteins), Journ. of biol. Chem., 3. 



2 Zeitschr. f. Biologie, 21. 



