860 PHYSIOLOGY OF DIGESTION AND SECRETION. 



logical conditions in which there is an increased breaking down of 

 tissues the creatinin excretion is increased.* Creatinin is present 

 in small amounts in the blood, 1 to 2 mgms per 100 gms. of blood, 

 and in somewhat larger amount in the muscular tissue. Creatin, 

 on the other hand, is present in muscular tissue to a relatively large 

 per cent., 0.5 to 0.6 gm. per 100 gms. of muscle, although Folin 

 contends t that this large yield is due to postmortem changes and 

 that in the living muscle little or none is present in free condition. 

 Creatin occurs in the blood in small amounts, but in the urine it is 

 not normally present so far as the normal adult man is concerned. 

 In children, however, it is constantly .present in the urine, and in 

 women it is said to occur after menstruation, during pregnancy, 

 and in the puerperium.t So also in mankind the urine shows the 

 presence of creatin during starvation or in fevers. It has not been 

 found possible to interpret satisfactorily these various facts. 

 According to one view, the creatin and creatinin are related and 

 have a common physiological significance in regard to the metabo- 

 lism. The creatin is regarded as an end-product of the break-down 

 of organized or living protein tissue. It is produced constantly in 

 the tissues and is normally converted to creatinin before it is ex- 

 creted in the urine. Under exceptional conditions, such as starva- 

 tion or fever, the disintegration of the tissues is increased and the 

 amount of creatin produced is too large to be wholly changed to 

 creatinin, with the .result that both creatin and creatinin appear in 

 the urine. Other observers If believe that the metabolic history and 

 significance of creatin and creatinin are different. The creatinin 

 formed in the tissues represents an end-product of the breaking 

 down of the organized tissue and, indeed, forms an index of the 

 amount of this tissue wear and tear, but it is given off to the blood 

 and excreted in the urine as creatinin. The creatin, on the con- 

 trary, while also constantly formed in the tissues as a result of their 

 metabolism, is not converted to creatinin, but undergoes some fur- 

 ther and as yet unknown metabolic change. When creatin is fed 

 to a man, for example, it is not excreted in the urine as creatin or 

 as creatinin, but is used in some way in the body. On this view 

 the significance of the creatin remains undetermined) and its 

 genesis and fate are also left unsettled, except so far as to deny its 

 conversion to creatinin. 



Hippuric Acid. This substance has the formula C 9 H 9 N0 3 . Its 



*Hoogenhuyze and Verploegh, "Zeitschrift f. physiol. Chemie," 57, 161, 

 1908. 



t Folin and 



j Krause, 



Mendel 

 also Meyers and Fine, ibid., 15, 283, 1913. 



1[ Folin and Krause, loc. cit.; also Benedict and Osterberg, "Journal of 

 Biological Chemistry," 18, 195, 1914. 



