PHYSIOLOGICAL CHEMISTRY 353 



Note red colour, due to picramic acid. Creatinin is now present. (For 

 other tests for creatinin see chapter on Urine.) 



The exact relationship of creatin to creatinin in the body is still 

 a matter of doubt. It was thought at one time that the creatin of the 

 muscles gave rise to the creatinin of the urine. This now appears not 

 to be the case, since creatinin is never present in muscle even after very 

 prolonged muscular exercise. The amount of creatinin in the urine is 

 extremely constant under all conditions, and it is therefore regarded 

 by Folin as a measure of the endogenous metabolism of the body. 

 Whence it arises is not certain, but the recent work of Mellanby points 

 to the fact that creatinin is formed in the liver from unknown pre- 

 cursors. From the creatinin thus formed the creatin supply of the 

 body is replenished, and the creatinin that is not wanted is excreted by 

 the kidney in the urine. We thus see that creatinin probably gives rise 

 to the creatin of the body, and not the creatin to the creatinin. 

 Further work is required to amplify these facts and also to find out 

 the fate of creatin in the body, which is at present unknown. 

 Recently Cathcart has pointed out that creatin, which does not 

 normally appear in the urine, is present when the carbohydrate 

 supply of the body is cut off. (See also small print at end of chapter.) 



Hypoxanthin and Xanthin. These are members of the group of 

 bodies known as the purin bodies. They are thus termed because the 

 so-called purin ring 



N C 



i LN X 



... ,: . - UU^" C . . 



is the basis of their constitution, purin itself, a synthetic body being 



N=C H 

 H C C NR 



' ' U-* 



or more simply C 5 H 4 N 4 



Hypoxanthin is monoxypurin, and is represented by the formula 

 HN C=0 



H C C N] 



