THE CHEMISTRY OF THE ANIMAL BODY. 553 



C 5 H 4 N 4 3 C 5 H 4 N 4 2 5 H 4 N 4 O C 5 H 4 N 4 . 



Uric acid. Xanthin. Hypoxanthin. Purin. 



To purin is given the following formula : 



N = C — H IN — 6C 



H — C C-XH 20 50 — N7 



\ 



\ 

 N— C— N '' 3N — 40- 



Purin. Purin nucleus 



// Q - 



For the convenience of chemical description the atoms of the purin 

 nucleus are numbered as above, since the chemical constitution varies with 

 the locality to which the atoms are attached to the nucleus. The purin deriv- 

 atives number many hundreds, but only about a dozen are known at present 

 to have physiological significance. 



Hypoxanthin is 6-oxypurin, xanthin is 2, 6-dioxypurin, uric acid is 

 2, 6, 8-trioxypurin, adenin is 6-amino-purin, while guanin is 2-amino- 

 6-oxypurin. 



Hypoxanthin, xanthin, adenin, and guanin are decomposition products of 

 the nucleins, and from their oxidation uric acid is derived. 



(a) Purins. 



Purin, C 5 H 4 N 4 . This, according to Emil Fisher, is a substance which 

 may occur in the body, but which on account of its ready decomposition has 

 not yet been discovered there. 



(6) Monoxypurins. 



NH — C = 



I I 



Hypoxanthin, or Sarcin, H — C C — NH\ 



|| || C — H.— This is found 



N — C— N 



in small amount in the tissues and fluids of the body and in the urine. 

 Hypoxanthin is derived from some nucleins, especially those contained in 

 the sperm of salmon and carp, through the action of water or dilute acids. 



(c) DlOXYPURINS. 



NH — = 



I I 



Xanthin, O = C C — NH \ 



C — H. — This substance, like hvpoxan- 



NH — C— N 



thin, is found in the tissues and fluids of the body and in the urine. It is a 

 decomposition product of some nucleins and may be found in those of the 

 pancreas, thymus, testicle, carp sperm, dr. 



Methyl Dioxypurins— The alkaloids theophyllin, theobromin, and caffein occur in 

 tea, coffee, cocoa, etc., and are habitually taken in the food. Theophyllin ( 1. 3-dimethyl- 



