872 PHYSIOLOGY 



Somewhat similar conditions apply to the oxidation of tryptophane. 

 This body is an indol derivative and consists of a benzene ring 

 and a pyrrol ring having two of their carbon atoms in common. Its 

 formula is 



^ CH \ 



HC C --- C.CH 2 CHNH 2 .COOH 



I II II 



HC C CH 



i.e. it is indol amino-propionic acid. It undergoes, like tyrosine, 

 complete oxidation in the body. On the other hand, a very slight 

 alteration in the molecule renders it incapable of this change. Thus 

 the trytophane set free by the tryptic digestion of proteins under the 

 influence of the putrefactive bacteria of the intestine may undergo 

 deamination and reduction with the production of indol propionic 

 acid, and this by oxidation may be converted to indol acetic acid. 

 The latter substance by decarboxylation may be converted into skatol, 

 or by oxidation nearer the chain and further loss of carbon dioxide 

 into indol. Of these products of bacterial change, indol acetic acid 

 may be found in the urine, and indol and skatol are oxidised to the 

 corresponding phenols and pass into the urine conjugated either with 

 sulphuric acid or with glycuronic acid. Apart, however, from these 

 putrefactive changes due to bacteria, no indol derivatives pass into 

 the urine. The amount of the indol and skatol esters serves therefore 

 merely as an index of bacterial decomposition in the alimentary canal, 

 and gives us no clue to the total tryptophane metabolism of the body. 

 If putrefaction be prevented by the administration of calomel or 

 other intestinal antiseptic these esters may entirely disappear from 

 the urine. On the other hand, the partial obstruction to the onward 

 passage of food, caused by dividing the small intestine in two places 

 a few inches apart and replacing the intervening length of intestine 

 the wrong way round, causes the indican excretion to be increased 

 twenty or thirty fold. Subcutaneous injection of tryptophane in 

 rabbits does not increase the indoxyl and skatoxyl sulphates (urinary 

 indican) in the urine, whereas a considerable increase is brought about 

 by subcutaneous injection of indol. 



The pyrrol ring which occurs in proteins as proline and oxyproline 

 (i.e. pyrrolidine carboxylic acid and oxypyrrolidine carboxylic acid) 

 appears to undergo complete disintegration in the body. The steps 

 in this conversion are unknown, though it is possible that the ring 

 may be unlinked so as to produce from the pyrrol ring amino-valerianic 

 acid, which would then undergo the process of deamination with which 

 we are already familiar. This ring is of interest since it appears to 



