310 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



In the small intestine the secretions are all alkaline, and it was formerly 

 taken for granted that the intestinal contents an' normally alkaline, [fthis were 

 so, the bacteria would find a favorable environment. It was supposed that 

 putrefaction of the proteids mighl occur, especially during the act of tryptic 

 digestion, and this supposition was home out by the extraordinary readiness of ar- 

 tificial pancreatic digestions to undergo putrefaction when not protected in some 

 way. Two recent cases ' of fistula of the ileum at its junction with the colon in 

 human beings have given opportunity for exact study of the contents of the 

 small intestine. The results are interesting, and to a certain extent are opposed 

 to the preconceived notions as to reaction and proteid putrefaction which have 

 just been stated. They show that the contents of the intestine at the point 

 where they are about to pass into the large intestine are acid, provided a mixed 

 diet is used, the acidity being due to organic acids (aeetie) and being equal to 

 0.1 per cent, acetic acid. These acids must have come from the bacterial fer- 

 mentation of the carbohydrates, and a number of bacteria capable of producing 

 such fermentation were isolated. The products of bacterial putrefaction of the 

 proteids. on the contrary, were absent, and it has been suggested that the acid 

 reaction produced by the fermentation of the carbohydrates serves the useful 

 purpose, under normal conditions, of preventing the putrefaction of the pro- 

 teids. With reference, therefore, to the point we are discussing — namely, the 

 bacterial decomposition of the contents of the intestines — we may conclude, 

 upon the evidence furnished by these two cases, that in the human being, when 

 living on a mixed diet, some of the carbohydrates undergo bacterial decompo- 

 sition in the small intestine, but that the proteids are protected. We may 

 further suppose that in the case of the proteids the limits of protection are 

 easilv overstepped, and that such a condition as a large excess of proteid in the 

 diet or a deficient absorption from the small intestine may easily lead to exten- 

 sive intestinal putrefaction involving the proteids as well as the carbohydrates. 



In the large intestine, on the contrary, the alkaline reaction of the secretion 

 is more than sufficient to neutralize the organic acids arising from fermentation 

 of the carbohydrates, and the reaction of the contents is therefore alkaline. 

 Here, then, what remains of the proteids undergoes, or may undergo, putrefac- 

 tion, and this process must be looked upon as a normal occurrence in the large 

 intestine. The extent of the bacterial action upon the proteids as well as the 

 carbohydrates may vary widely even within the limits of health, and if excessive 

 may lead to intestinal troubles. Among the products formed in this way, the 

 following are known to occur: Leucin, tyrosin, and other amido-acids ; indol ; 

 skatol ; phenols; various members of the fatty-acid series, such as lactic, 

 butyric, and caproic acids; sulphuretted hydrogen; methane; hydrogen; 

 methyl mercaptan, etc. Some of these products will be described more fully 

 in treating of the composition of the feces. To what extent these products 

 are of value to the body it is difficult, with our imperfect knowledge, to say. 

 It ha- been pointed out, on the one hand, that some of them (skatol, fatty 



1 Macfayden, Ncncki, and Sieber: Archivfur experimentelle Pathologie u. Pharmakologie, 1891' 

 Bd. 'J- 1 , S. 311 ; Jakowski : Archives des Sciences biologiques, St. Petersburg, 1892, t. 1. 



