110 PHYSIOLOGY FOR DENTAL STUDENTS. 



really the reverse of that which occurs in the organism and rep- 

 resented by the above formulas. This change occurs in urine and 

 accounts for the ammoniacal odor which develops when this fluid 

 is allowed to stand. 



CREATININ. This is very closely related to creatin, which is the 

 most abundant extractive substance in muscle, and which yields 

 urea when it is boiled with weak alkali. These chemical facts 

 would lead us to expect that some relationship must exist be- 

 tween the creatin of muscle and the creatinin and urea of urine, 

 but, so far, it has been impossible to show what this relationship 

 is. One very important fact has, however, been brought to light, 

 namely, that creatin makes its appearance in the urine when 

 carbohydrate substances are not being oxidized in the body, as 

 in starvation, and in the disease diabetes. This is one reason for 

 the growing belief that carbohydrates are something more than 

 mere energy materials (see p. 113). The excretion of creatinin 

 is so remarkably independent of the amount of protein in the 

 food that it is believed to represent more especially the end prod- 

 uct of the protein break-down of the tissues themselves, in con- 

 trast to urea, which partly represents the cast-off nitrogen of the 

 protein of the food. 



PURIN BODIES. These are of particular interest because they 

 include uric acid, about which more nonsense has been written 

 than about any other product of animal metabolism. The so- 

 called uric acid diathesis is very largely a medical myth a cloak 

 for ignorance. Uric acid is the end oxidation product of the 

 purin bodies, which include the hypoxanthin and xanthin of 

 muscle and their amino derivatives, the adenin and guanin of 

 nuclein. 



These relationships are seen in the following formulas : 



Oxy purins of muscle . . . I Hypoxanthin C 5 H 4 N 4 



{ Xanthin C 5 H 4 N 4 0, 



Amino purins of nuclein. . 1 Adenin C 5 H 4 N 4 NH 



( Guanin C 5 H 4 N 4 ONH 



Uric acid C 5 H 4 N 4 2 



There are therefore two sources for uric acid in the animal 



