THE CHEMISTRY OE THE ANIMAL BODY. 571 



amount of homogentisic acid. It may arise from the reduction and oxidation of tyrosin 

 according to the following reaction: 1 



+ H 2 



OH/ \ NH 3 +C0 2 + 2H 2 



+ 50 2 = 



'oh 



CH 2 CHNH 2 COOH CH 2 COOH 



Pyridin.— This hody has the accompanying formula, one of the CH groups in benzol 

 H 

 C 



HC CH 



being substituted by N : || • When pyridin is fed, methyl-pyridin ammonium 



HC CH 



V 



hydroxide, OH.CH 3 .NC 5 H 5 , is excreted in the urine. 2 This is another case, besides those 

 of selenium and tellurium, of methylation in the body. 



H H 



C C 



HC C CH 

 Chinolin. — The accompanying formula illustrates the composition 



HC C CH 



N C 

 H 

 of this body. Several of the methyl-chinolins burn readily in the body. 3 



Cynurenic Acid, C 9 H 5 N.OH.COOH.— This is oxychinolin carbonic acid ; it is found 

 normally in dog's urine, being derived from proteid in amounts proportional to proteid 

 metabolism. It is, however, not derived from the metabolism of gelatin, 4 a body which 

 does not yield the aromatic chain. 



Indol, or Benzopyrol, C 8 H 7 N. — The source of indol is surely from 

 proteid putrefaction; it may also be obtained by melting proteid with potash. 



H H 



C C 



// \ /\ // \ y\ 



HC C CH HC C COH 



I II II I II II 



HC C CH HC C CH 



^/\/ % /\/ 



C N C N 



H H H H 



Indol. Indoxyl. 



After its absorption it receives an oxy- group ju>t as benzol docs, and like 

 benzol pairs with sulphuric acid with the loss of a molecule of water, and 

 appears as ethereal sulphate in the urine. In preparing indol from feces the 

 fecal odor clings to it. Pure indol, however, has no smell. An alcoholic 



'Enibden: Zeittehrift fur physiologiscke Chemie, 189:2, I5d. 17, 8. 182. 



2 His: Archiv fur exper. Pathologie wad Pharmafcologie, 1887, I'«d. 22,8.263. 



3 Cohn: Zeiischrift fur phymlogische Chemie, 1804, I'.d. 20, S. 210. 



* Mendel and Jackson : American Journal of Physiology, 1899, vol. ii. p. 1. 



