172 PHYSIOLOGY OF ALIMENTATION. 



Our knowledge of the bacterial products present in the 

 small intestine of the human being has been derived from 

 analyses of intestinal contents obtained from patients suf- 

 fering from intestinal fistulse. The observers who have 

 worked in this field all agree that the contents of the small 

 intestine are acid in reaction, determined, however, not by 

 free hydrochloric acid, but by fatty acids resulting in the 

 main from the activity of the lipase produced by the pancreas 

 and the intestinal wall upon the fats of the food, but also in 

 part due to the action of lipase-containing bacteria. No in- 

 considerable amount of acid seems to be derived from the 

 carbohydrates through the action upon them of the bacteria 

 found in the small intestine. Among the acids formed in 

 this way in small amounts under normal conditions, and in 

 often enormous amounts in pathological states may be men- 

 tioned acetic, different kinds of lactic, succinic, butyric, and 

 formic acids. The excessive formation of these acids is at 

 once brought about when from any cause such as insuf- 

 ficiency of the secretions of the alimentary tract, or insuf- 

 ficiency of the proper ferments in these secretions, or enjoyment 

 of excessive amounts of carbohydrates these are not digested 

 and absorbed in the proper way and so become the prey of 

 the bacteria always present here. The formation of small 

 amounts of these organic acids need not be followed by se- 

 rious consequences. Small amounts may be absorbed, oxi- 

 dized in the tissues, and no evil consequences result. Others 

 undergo further change in the alimentary tract and are con- 

 verted into water, carbon dioxide, marsh-gas, and hydrogen. 

 The organic acids produced bring about, even in small amounts, 

 an increased peristalsis and an increased secretion of water 

 into the intestine, so that if the condition is at all marked, 

 frequent liquid stools, acid in reaction and ill-smelling, result. 

 The presence of gases in the intestines also induces peristalsis. 

 It is clear that a slight alimentary fermentation need not 

 be an evil thing. Unquestionably the beneficent effects of 

 the addition of vegetables to an ordinary mixed diet in bring- 



