THE ORGANIC CONSTITUENTS OF THE URINE. 257 



water. The solution is decolorized with animal charcoal, filtered 

 while hot, and the filtrate acidified slightly with hydrochloric acid. 

 On standing, the allantoin separates out. 



Kreatin and Kreatinin. 



According to older concepts kreatin is a waste product of the 

 protein metabolism and transformed in the body into its " anhydride " 

 kreatinin and is thus eliminated in the urine. Folin and Klercker 

 have shown, however, that this view is erroneous. Folin has pointed 

 out that the transformation of the one substance into the other is 

 not at all so easily accomplished as was formerly supposed and that 

 kreatin fed by the mouth is not eliminated in the urine as kreatinin, 

 while the introduction of the latter gives rise to a corresponding 

 increase of the normal kreatinin in the urine. With the experi- 

 mental subject on a diet poor in nitrogen Folin could show that the 

 ingested kreatin is not eliminated either in the feces or the urine 

 and is apparently largely retained in the body. To a certain de- 

 gree this occurs also when the subject is placed on a diet rich in 

 proteins. It accordingly appears that kreatin may be an important 

 factor in the nitrogenous metabolism and can in a certain sense be 

 viewed as a foodstuff. Further research, however, is necessary to 

 clear the situation. When administered in excess a fraction appears 

 in the urine as such. It then gives rise to the formation of neither 

 kreatinin nor of urea. 



Kreatinin, according to Folin, is the essential end-product of the 

 endogenous nitrogenous katabolism, in so far at least as the muscle 

 tissue is concerned. He has demonstrated the interesting fact that its 

 absolute quantity eliminated on a meat-free diet is a constant quantity, 

 which is different for different individuals, but wholly independent 

 of quantitative changes in the total amount of nitrogen eliminated. 

 Its relative amount is increased when the urea nitrogen falls. On 

 a diet rich in proteins the kreatinin nitrogen represents 3.2-4.5 

 per cent, of the total, while on one free from proteins (starch and 

 cream) the amount may rise to 17.4 per cent. The absolute amount 

 seems to depend to a certain extent upon the body weight. Fat or 

 corpulent persons yield less kreatinin per unit of body weight, 

 namely 20 mgrms. per kilo, while lean persons yield about 25 mgrms ; 

 1.15-1.6 grammes may thus be regarded as average values. 



The study of pathological variations in the amount of kreatinin 

 has been greatly facilitated through the introduction of Folin's 

 method (see below). The older data are of little importance, unless 

 the diet of the individual has been carefully considered. A diet 

 rich in meat, it should be borne in mind, greatly increases the 

 amount. 



Properties. Kreatin crystallizes in colorless, highly refractive 

 monoclinic prisms, and is quite soluble in hot and cold water, less 



17 



