BACTERIAL DIGESTION. 253 



tions of the whole region of antiperistalsis. These contractions 

 squeeze the material toward the end of the transverse colon where 

 slowly-moving peristaltic waves force it to the rectum." 



These movements, as in the case with the stomach and small 

 intestine, are inhibited by rage, anxiety, or distress. 



BACTERIAL DIGESTION. 



Bacteria are found in considerable numbers in the mouth, 

 stomach, and intestine ; more than sixty species are recorded 

 by Sternberg as having been found in the mouth ; and seventy- 

 four have been isolated from feces and the intestines of cadavers. 

 Those which occur in the stomach consist of mouth-bacteria which 

 have been swallowed together with bacteria which are in the food 

 and drink. We have already referred to some of the pathogenic 

 or disease-producing bacteria, and the effect of hydrochloric acid 

 upon them (p. 196). But besides these there are others which have 

 a true digestive action on the food-stuffs. Inasmuch as there is no 

 free hydrochloric acid in the stomach for about half an hour after 

 food has entered it, the antiseptic action of this acid is not exerted 

 for that length of time, and the conditions are favorable for bacterial 

 action. During this time some of the carbohydrates may be decom- 

 posed, with the result of producing lactic and other acids and set- 

 ting free hydrogen gas. Proteids do not, however, appear to be 

 acted upon by bacteria in the stomach. In the small intestine 

 there is some decomposition of proteids, but not to any considerable 

 extent. Lactic and other organic acids are, however, produced 

 from carbohydrates. These changes in both proteids and carbo- 

 hydrates are due to the action of bacteria. 



The action of the intestinal bacteria upon proteids has been 

 likened to that of trypsin. The proteid is dissolved, and then 

 changed into albumoses and peptones. A part goes on to the 

 stage of tyrosin, which becomes still further decomposed into 

 paraoxyphenylpropionic acid, paraoxyphenylacetic acid, phenol, 

 and parakresol. From another portion of the proteid are 

 formed indol, skatol, and skatolcarbonic acid. These substances 

 are not derived from tyrosin nor, indeed, from peptones, but 

 from some unknown intermediate substance derived from the 

 proteid itself. 



All of the carbohydrates of the food seem to be subject to 

 bacterial action. Thus starch and even cellulose may be decom- 

 posed by the appropriate bacteria. As results of carbohydrate 

 decomposition are produced ethyl alcohol, lactic, butyric, and 

 succinic acids, together with carbon dioxid and hydrogen. 



The fats are normally unchanged by bacterial action ; in the 

 absence of bile or pancreatic juice they are decomposed, with the 

 formation or fatty acids. 



It is claimed that one important office performed by the intesti- 

 nal bacteria is to prevent putrefaction. 



