CHAP. X.] PRODUCTS OF BACTERIAL DECOMPOSITION OF PROTEIDS. 419 



factive processes in the small intestines, and especially to prevent the 

 formation of those foetid products which are the essence of the putre- 

 factive process. In discussing the disinfecting function of the bile it 

 was argued that this fluid probably exerts a real disinfecting action, 

 as Maly and Emich have contended, in virtue of the bile acids which 

 it contains, though Yoit and Rohmann deny this special action. 



Macfadyen, Nencki, and Sieber have shewn that, contrary to the 

 general belief, but in accordance with many previous observations by 

 reliable investigators, the contents of the small intestine are invari- 

 ably acid 1 . The presence of free acid in the small intestine acts 

 doubtless both by setting free the antiseptic bile acids and by the 

 destructive and inhibitory influence which free acids exert on many 

 forms of bacterial life. 



Accordingly, the above-named observers have found that in the 

 small intestine of man the products of the putrefactive decomposition 

 of proteids are absent, the organisms which are able to occasion their 

 decomposition being absent. Although, as has been argued, the 

 putrefactive processes in the small intestine are, in the perfectly 

 physiological condition, comparatively insignificant in amount, we 

 must yet consider them in some detail, inasmuch as they play a 

 much more important part in disease, and are, besides, constant 

 products of the processes which occur in the large intestine. 

 Processes of fermentation affecting the carbohydrates, as distin- 

 guished from putrefactive processes, normally occur on a considerable 

 scale in the small intestine. 



SECT. 1, THE DECOMPOSITION OF THE PROTEIDS UNDER THE 

 INFLUENCE OF BACTERIAL ACTION. 



In discussing the action of trypsin on the albuminous bodies we 

 have shewn that, in addition to the albumoses and peptones, there 

 result, from the profoundly decomposing action of that enzyme, many 

 amido-acids of the fatty group, paroxyphenylamidopropionic acid or 

 tyrosine, certain bases (lysine, lysatinine and ammonia), and a 

 chromogen which we designate tryptophan. Although there is 

 evidence that the complex albuminous molecule contains a variety of 

 aromatic groups, it is noteworthy that the only primary aromatic 

 compound which results from the action of trypsin is tyrosine. 

 Under the influence of the putrefactive bacteria, the same products 

 are at first formed. Other bodies, however, rapidly arise, certain of 

 which (aromatic oxy-acids and phenols) are the products of decom- 

 position, reduction, and oxidation, of tyrosine, whilst others (indol, 

 methyl-indol or skatol, skatol-carbonic acid) are aromatic compounds 

 which are not directly related to tyrosine and which represent a 



1 A. Macfadyen, M. Nencki and N. Sieber, ' Untersuchungen iiber die chemischen 

 Yorgange im menschlichen Diinndarm,' Archiv f. exp. Path. u. Pharm. Vol. xxvin. 

 (1891), p. 311. 



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