THE BACTERIA OF THE ALIMENTARY TRACT. 169 



A discussion of the products of bacterial activity in the 

 alimentary tract is therefore next in order. Without enter- 

 ing too deeply into the chemical changes which the indi- 

 vidual varieties of bacteria are capable of producing in the 

 intestinal contents, the alimentary flora as a whole may 

 be looked upon as able to bring about the following well- 

 established decompositions. The amount of such decom- 

 positions is, of course, again dependent upon a large num- 

 ber of external conditions, of which we need mention by 

 way of illustration only the character and amount of food 

 consumed, the length of time that such food remains in 

 the intestinal tract, the reaction of the intestinal contents 

 as determined by physiological or pathological variations 

 in the secretions poured out upon the food, etc. 



The bacteria of the alimentary tract contain in their 

 bodies or secrete, first of all, a number of enzymes which 

 are not unlike those which are normally poured out upon 

 the food in its passage from mouth to anus. We need 

 mention here only amylase, sucrase, and lactase, which 

 like the ferments normally poured out upon the food con- 

 vert starch into maltose, cane-sugar into dextrose and 

 laevulose, and milk-sugar into dextrose and galactose. Pro- 

 teolytic enzymes probably identical with acid- and alkali- 

 proteinase (pepsin 'and trypsin) are also found in the ali- 

 mentary bacteria. By virtue of these they not only split 

 proteins into albumoses and peptones but even into the 

 ultimate digestion products (mono- and diamino-acids) 

 with which we have already become acquainted in the dis- 

 cussion of the proteolytic enzymes found in the alimentary 

 secretions proper. Lipase is also found in certain of the 

 intestinal bacteria, so that the presence of fatty acid in 

 the intestinal contents must be attributed at least in part 

 to the activities of these micro-organisms. At one time the 

 presence of fatty acids in the stomach in cases of carci- 

 noma and other diseases which may be associated with a 

 decreased amount or entire lack of hydrochloric acid was 



