414 



METABOLISM, NUTRITION, AND DIET 



an appreciable quantity, even when living on an exclusively animal diet. 

 Hippuric acid is formed from the union of benzoic acid with glycin 

 (C 2 H 5 NO 2 + C ? H 6 O 2 = C 9 H 9 NO 3 + H 2 O), which union takes place under 

 experimental conditions in the kidneys themselves. 



The source of the nitrogenous extractives of the urine is chiefly from the 

 metabolism of the nitrogenous foods and tissues, but we are unable to say 

 whether these nitrogenous bodies have merely resisted further decomposition 

 into urea, or whether they are the representatives of the decomposition of 

 special tissues, or of special forms of metabolism of the tissues. There is, 

 however, one exception, and that is in the case of creatinin. This represents 

 not only the creatinin which enters the body in ordinary flesh food, but is a 

 nitrogenous v/aste which Folin regards as a measure of muscle metabolism. 

 The creatinin eliminated is almost a constant quantity in a given individual, 

 irrespective of the quantity of proteid in the diet. Koch has attempted to 

 trace a quantitative relation of creatinin excretion to lecithin in the food. 



THE METABOLISM OF FATS. 



Fats, with carbohydrates, are the direct source of most of the energy 

 manifested by the body, a fact demonstrated by numerous observations. 



The Energy Value of Fats in Metabolism. Fats, in comparison 

 with other food principles, are of especial value as sources of energy. They 

 are completely oxidized in the body to carbon dioxide and water, and yield, 

 therefore, as much energy to the body as they yield upon oxidation outside 

 the body. The energy equivalent of one gram of fat is 9.3 large Calories, 

 more than twice that of starch or of proteid, which in the body yield only 

 4.1 Calories each per gram. 



A study of the elimination of nitrogen and of carbon during fasting shows 

 that the fats contribute to energy formation for many days. This is illus- 

 trated by the following computation by Voit: 



METABOLISM IN A DOG DURING FASTING. (Vorr.) 



The amount of fat metabolized is sharply influenced by the amount and kind 

 of other food. For example, if the amount of fat metabolized per day in 

 fasting is first determined, then a ration of proteid given for a few days, 

 followed by a second fasting period, it will be found that the metabolism of 



