EXCRETIONS 493 



Creatin. Creatin is methyl guanidin acetic acid. 



UN = C 



CH 3 .N CH 2 COOH 



It is a constant constituent of striated muscle, the concentration in man 

 heing about 0.39 per cent. The creatin content of striated muscle appears 

 to be both constant and distinctive for a given species (see preceding arti- 

 cle, p. 401). Creatin is also present in heart muscle in about two-thirds the 

 concentration of striated muscle and in the testis, brain, smooth muscle 

 and liver in much lower concentrations, the figures varying from about 0.1 

 per cent in the testis and brain to 0.3 per cent in the smooth muscle of 

 the intestine and uterus, and slightly less in the liver. 



Folin, in his original discussion of the subject, pointed out that 

 although creatin is normally absent, from urine, occasionally small amounts 

 may be detected. This phase of the problem received renewed interest 

 when F. G. Benedict (c) noted in starvation experiments on man that con- 

 siderable quantities of creatin appeared in the urine. Following up this 

 observation, Benedict and Myers observed the elimination of varying 

 amounts of creatin in a large number of undernourished insane patients. 

 Subsequent observers have shown that creatin is regularly excreted par- 

 ticularly in carcinoma of the liver, diabetes, muscular dystrophy, exoph- 

 thalmic goiter, anterior poliomyelitis, pernicious vomiting of pregnancy, 

 typhoid fever and pneumonia. In all except the last two conditions 

 mentioned (fevers) this is accompanied by a lowered creatin in output, 

 and even in fevers this is true during convalescence. Judging from the 

 observations of Denis on the creatin content of human muscle obtained at 

 autopsy, it would appear that the excretion of creatin was generally 

 associated with a low muscle content. In carcinoma of the liver the 

 creatin elimination may be very large, 1-1.5 grams. 



From the foregoing, it would appear that the excretion of creatin 

 was pathological, but Rose, and also Folin and Denis (6), have recently 

 observed the interesting fact that growing children excrete creatin while 

 according to Krause normal women periodically excrete small amounts 

 of creatin. 



Muscle creatin has quite generally been regarded as the source of the 

 urinary creatin in starvation and pathological conditions associated with 

 undernutrition, although some workers have opposed this view. In the 

 case of starving rabbits Myers and Fine(<7) believed that they were able to 

 account for the creatin lost from the muscle on the basis of urinary 

 findings, but these observations can hardly be directly compared with 

 pathological conditions in the human subject. McCollum and Steenbock 



