INTESTINAL DIGESTION. 77 



of benefit to the health of man because when it occurs other bac- 

 teria which are more harmful than useful become destroyed. To 

 encourage this growth of lactic acid bacteria, it has been recom- 

 mended that large quantities of sour milk should be taken. It is 

 undoubtedly true that such treatment is of benefit in many per- 

 sons who suffer from excessive intestinal putrefaction, but that 

 such treatment should prolong the life of otherwise healthy indi- 

 viduals is visionary. As in herbivora, there are also bacteria in 

 man which break up cellulose, producing methane and C0 2 . After 

 diets containing much vegetable matter, therefore, a large 

 amount of gas is likely to accumulate in the intestines. From 

 fats, the intestinal bacteria produce lower fatty acids, which 

 tend to cause the contents in the lower portion of the small in- 

 testines to become acid in reaction. 



Although capable of hydrolyzing native protein from the very 

 start, bacteria act more readily on protein that has been partially 

 digested by the proteolytic enzymes of the stomach and intes- 

 tines. The products of this action are more or less characteristic 

 because of the peculiar manner in which the aromatic groups of 

 the protein molecule are attacked, producing from it such sub- 

 stances as phenol, skatol, indol, etc., to which the characteristic 

 odor of the fasces is due. "When protein has been adequately di- 

 gested in the stomach, it is so rapidly acted on by the trypsin 

 (and erepsin) of the small gut and is so quickly absorbed that 

 bacteria have no chance to act on it. When protein has been in- 

 adequately digested in the stomach, however, the trypsin fails to 

 digest it quickly enough, so that bacterial putrefaction sets in 

 which may be quite marked in the small intestine, although much 

 more so in the colon. Even when they do not find a suitable sub- 

 strat in the food, the bacteria attack the proteins of the intes- 

 tinal secretions themselves, which accounts for the well-known 

 occurrence of this process during starvation. 



The Immunity of the Walls of the Digestive Organs Toward 

 the Enzymes Which Act within Them. The immunity of the 

 mucosa of the stomach and intestines seems to be due in main to 

 the presence in the cells of the mucosa of anti-enzymes, that is of 

 substances which can inhibit the action of the various enzymes 



