394 CHANGES IN THE SMALL INTESTINE. [Book ii. 



results modified by or mixed with the results of the action of 

 micro-organisms. We spoke above, § 208, of bile as being anti- 

 septic, but this must be understood as meaning not that the 

 presence of bile arrests the action of all micro-organisms within 

 the intestine, but that it modifies their action, keeping it within 

 certain limits and along certain lines. 



Concerning the exact nature and extent of the changes thus 

 due to micro-organisms our knowledge is at present very im- 

 perfect. The proteids and the carbohydrates seem to be the 

 food stuffs on which these organisms produce their chief effect. 

 Out of the proteids they give rise not only to indol but to several 

 other compounds, among which may be mentioned phenol 

 (C 6 H 6 0), of which a small quantity may be recognized in the 

 fasces, the rest being absorbed and appearing in the urine in 

 the form of certain phenol-compounds, such as phenyl-sulphuric 

 acid. Out of proteids they may also form the peculiar poison- 

 ous bodies called ptomaines, which appear in the ordinary putre- 

 faction of proteids. But their most conspicuous effects are 

 those on the carbohydrates. As the food descends the intestine, 

 the presence of lactic acid becomes more and more obvious; 

 indeed in some cases the naturally alkaline reaction of the in- 

 testinal contents may in the lower part of the intestine be 

 changed into an acid one by the presence of lactic acid. Now 

 lactic acid may be formed out of sugar by means of a special 

 organism inducing what is spoken of as the lactic acid fermen- 

 tation. And we have every reason to believe that in even 

 normal digestion, a certain quantity of sugar, either eaten as 

 such, or arising from the amylolytic conversion of starch, does 

 not pass away from the intestine into the blood as sugar, but 

 undergoes this fermentation into lactic acid. To what extent 

 this change takes place we do not know ; the amount probably 

 varies according to the amount of carbohydrates eaten, the con- 

 dition of the alimentary canal, and other circumstances. It 

 may be under certain circumstances simply a part of normal 

 digestion ; under other circumstances it may be excessive and 

 give rise to troubles. 



That fermentative changes may occur in the small intestine 

 is further indicated by the facts that the gas there present may 

 contain free hydrogen, and that chyme after removal from the 

 intestine continues at the temperature of the body to produce 

 carbonic acid and hydrogen in equal volumes. This suggests 

 the possibility of the sugar of the intestinal contents under- 

 going the butyric acid fermentation during which, as is well 

 known, carbonic anhydride and hydrogen are evolved. By this 

 change the sugar is removed from the carbohydrate group into 

 the fatty acid group ; it is thus, so to speak, put on its way to 

 become fat. We shall see hereafter that sugar may be some- 

 ! ?re in the body converted into fat; this conversion however 



