260 LECTURE XII. 



contamination, without finding any ground for such an assumption. That, 

 on the contrary, carbon dioxide is split off by the action of putrefactive 

 bacteria, has been convincingly shown by Ellinger. 1 Cadaverine and 

 putrescine are only found in the faces and urine under exceptional condi- 

 tions, as, for example, in dysentery and acute enteritis. It is particularly 

 well known that these diamines appear in cystinuria, a disturbance in the 

 metabolism of albumin which we shall soon take up more in detail. It is 

 still questionable what the relation is between the appearance of these 

 two diamines and this metabolic irregularity. At all events, these com- 

 pounds are not always observed when cystine is eliminated in the urine. 

 We have now mentioned all those products of urine which are to be 

 traced to putrefaction in the intestines, and will now turn our attention 

 to an acid which has been found only in the urine of certain animals, 

 especially dogs, namely kynurenic acid, whose mother-substance has been 

 quite recently recognized to be tryptophane. It is y -hydro xyquinolin- /?- 

 carboxylic acid: 2 



HC C C . COOH 



I II I 



HC C CH 



The formation of kynurenic acid from tryptophane was proved by 

 Ellinger, who fed some of the tryptophane, inclosed in a gelatine capsule, 

 to a dog, and estimated the amounts of kynurenic acid before and after 

 the feeding. The increase caused by tryptophane, was very appreciable. 

 Rabbits, which ordinarily do not excrete any kynurenic acid, did so after 

 the administration of tryptophane. 3 Human beings, on the other hand, 

 were not found to produce any kynurenic acid. 



These decomposition products give us a very good idea of the protein 

 decomposition in the tissues. We will not go very far astray if we accept 

 the following conception of the behavior of the proteins in the animal or- 

 ganism. In the stomach, the albuminous substances are almost entirely 

 broken down into a number of very complicated products by the action of 

 pepsin and hydrochloric acid. These pass on to the intestine, where they 

 are attacked further by trypsin. Under these influences, polypeptides are 

 produced, a larger or smaller number of the amino acids entering into 

 their composition. A large number of free amino acids are split off at 

 the same time, first, tyrosine, tryptophane, and cystine. Then follow 



1 A. Ellinger: Z. physiol. Chem. 29, 34 (1900); Ber. 31, 3183 (1899); 32, 3542 (1900). 



2 J. Liebig: Ann. 86, 125 (1853). R. E. Swain: Am. J. Physiol. 13, 30 (1905). 



3 A. Ellinger: Z. physiol. Chem. 43, 325 (1904). 



