CHEMISTRY OF DIGESTION AND NUTRITION. 279 



eliminated in the urine as creatinin. It is evident, therefore, that part 

 of the creatinin of the urine is derived from the meat eaten, and does 

 not represent a metabolism within the body. A part, however, comes 

 undoubtedly from the destruction of proteid within the body. In this con- 

 nection the following facts are suggestive and worthy of consideration, although 

 they cannot be explained satisfactorily : The mass of proteid tissue in the body 

 is found in the muscles, and the end-product of the destructive metabolism of 

 proteid is supposed to be chiefly urea. Nevertheless, urea is not found in the 

 muscles, while creatin occurs in considerable quantities, as much as 90 grams 

 being contained in the body-musculature at any one time. Only a small 

 quantity (1.12 grams) of creatin is eliminated in the urine as creatinin during 

 a day. What becomes of the relatively large quantity of creatin in the mus- 

 cles? It has been suggested that it is one of the precursors of urea that it 

 represents an end-product of the proteid destroyed in muscle which is subse- 

 quently converted to urea in the liver or elsewhere. This supposition is sup- 

 ported by the fact that creatin may be decomposed readily in the laboratory, 

 with the formation of urea among other products. But against this theory 

 we have the important fact that creatin introduced into the blood is not con- 

 verted to urea, but is eliminated as creatinin. 



Hippuric Acid. This substance has the formula C 9 H 9 NO 3 . Its molecular 

 structure is known, since upon decomposition it yields benzoic acid and gly- 

 cocoll, and, moreover, it may be produced synthetically by the union of these 

 two substances. Hippuric acid may be described, therefore, as a benzoyl-amido- 

 acetic acid. It is found in considerable quantities in the urine of herbivorous 

 animals (1.5 to 2.5 per cent.), and in much smaller amounts in the urine of 

 man and of the carnivora. In human urine, on an average diet, about 0.7 

 gram is excreted in twenty-four hours. If, however, the diet is largely 

 vegetable, this amount may be increased greatly. These last facts are readily 

 explained. It has been found that if benzoic acid or related substances con- 

 taining this group are fed to animals, they appear in the urine as hippuric 

 acid. Evidently, a synthesis has taken place within the body, and Bunge and 

 Schmiedeberg proved conclusively that in dogs, and probably, therefore, in 

 man, the union of the benzoic acid to glycocoll occurs mainly in the kidney 

 itself. We can understand, therefore, why vegetable foods which are known to 

 contain substances belonging to the aromatic series and yielding benzoic acid 

 should increase the output of hippuric acid in the urine. Since, however, in 

 starving animals or in animals fed entirely on meat hippuric acid is still pres- 

 ent, although reduced in amount, it follows that it arises in part as one of the 

 results of body-metabolism. Among the various products of the breaking- 

 down of the proteid molecule, it is probable that some benzoic acid occurs, 

 and, if so, it is excreted in combination with glycocoll as hippuric acid. It 

 should be added, finally, that some of the hippuric acid is supposed to be de- 

 rived from the process of proteid putrefaction which occurs to a greater or 

 less extent in the large intestine. 



Conjugated Sulphates. A good part of the sulphur eliminated in the 



