FOODS — HUMAN NUTRITION. L67 



the excess being due to free organic acids." The excess of inorganic acids observed 

 in urine diminished under the influence of the Btarch and cream diet until it fre- 

 quently became a minus quantity. 



When potatoes replaced pure starch in the diet, " the total acidity of the urine is 

 but slightly reduced, and the total amount of organic a«-i< Is eliminated is greatly 

 increased, yet the ammonia is still considerable. This would seem to indicate that 

 a part of the acid and ammonia formation within the organism is not affected by the 

 alkalies of the food." 



A theory of protein metabolism, < >. Km. in (Amer. Jour. Physiol., IS {1905), 

 No. ?, pp. 117-188). — On the basis <>!' investigations noted above, various questions 

 connected with the metabolism of protein in the animal body are discussed. 



The fact that, generally Bpeaking, the proportion of urea to total nitrogen in the 

 urine diminished with a decrease in the amount of nitrogen consumed, while the 

 other nitrogenous constituents in the urine remained practically constant, led the 

 author to conclude thai there are 2 distinct processes of proteid metabolism in the 

 body. In Ins opinion the metabolic processes resulting in the end products which 

 tend to remain constant creatinin, neutral sulphur, and to a less extent uric acid 

 and ethereal sulphates) are needed for the continuation of life; or, in other words, 

 the metabolic processes which they represent constitute an essential part of the 

 activity which distinguishes living from dead cells. 



He, therefore, proposes the term "tissue" metabolism or "endogenous" metabo- 

 lism for this form of proteid cleavage, and "exogenous" or intermediate metabolism 

 for the proteid cleavage which is variable and yields chiefly urea and inorganic sul- 

 phates, this form of metabolism being looked upon as an attempt on the part of the 

 body to remove rapidly the surplus nitrogen supplied which is not required for vital 

 process - 



Attention is called to the fact that the nitrogen of protein is linked to carbon on 

 the one hand and to hydrogen on the other — i. e., exists as amido or imido groups— 

 and that from a chemical standpoint the cleavage of such groups is more readily 

 accomplished by hydrolysis than by oxidation. 



In the author's opinion exogenous proteid catabolism consists of a series of hydro- 

 lytic cleavage processes resulting in a rapid elimination of proteid nitrogen as urea. 

 "According to the views here presented . . . only a small amount of protein, 

 namely, that necessary for the endogenous metabolism, is needed. The greater 

 part of the protein furnished with standard diets like Voit's— i. e., that part repre- 

 senting theexogenous metabolism — is not needed, or, to he more specific, its nitrogen 

 i- not needed. 



"The organism has developed special facilities forgetting rid of such excess of 

 nitrogen so as to get the use of the carbonaceous part of the protein containing it. 

 The first step in this process is the decomposition of protein in the digestive tract 

 into proteoses, amido acids, ammonia, and possibly urea. The hvdroh tic decompo- 

 sitions are carried further in the mucous membrane of the intestines, and are com- 

 pleted in the liver, each splitting being such as to further the formation of urea. 



"In these special hydrolytic decompositions, the result of which is to remove the 

 unnecessary nitrogen, we have an explanation of why and how the animal organism 

 tend' to maintain nitrogen equilibrium, even when excessive amounts of protein are 

 furnished with the food. This excess of protein is not stored up in the organism, as 

 Rich, because the actual need of nitrogen is so small that an excess is always tur- 

 nished with the food, except, of course, in carefully planned experiments. The ordi- 

 nary food of the average man contains more nitrogen than the organism can use. and 

 increasing the nitrogen still further will therefore necessarily only lead to an imme- 

 diate increase in the elimination of urea, and doesnot increase the protein cat a hoi ism 

 involved in the creatinin formation any more than does an increased supply of fats 

 and carbohydrates. . . . 



