DIGESTION 137 



Normally its activity is arrested by the hydrochloric acid of 

 the gastric juice about twenty minutes after a meal. After 

 this no further multiplication of bacteria should occur. The 

 presence of bacteria which grow in a strongly acid medium 

 usually indicates that the stomach was not completely emptied 

 before fresh food reached it. It may be that the last meal 

 was too large or the interval too short. If the mucous membrane 

 is in an unhealthy condition, its own secretions afford material 

 on which bacteria thrive. Nothing short of washing it out 

 with a stomach-pump will clean it up. The presence, at the 

 time of feeding, of food left over from the previous meal is 

 likely to perpetuate the unsatisfactory state of affairs. All 

 the glands of the alimentary tract exhibit a tendency to 

 periodicity. Their efficiency is greatest when activity follows 

 a period of rest. If the stomach is not able to expel its contents, 

 it has not the opportunity of preparing for fresh duties. Fat 

 undergoes a certain amount of rancid fermentation in the 

 stomach. Proteins are not attacked by bacteria in the stomach 

 unless the condition of the organ is very unsatisfactory. The 

 odour of the products of their decomposition is then recog- 

 nizable in the breath. 



Bacteric fermentations in the small intestine are unimpor- 

 tant under normal conditions, with the exception of the 

 fermentation of cellulose. Cellulose has the same empirical 

 formula as starch. It is completely insoluble, and is not 

 affected by any of the digestive juices. The greater part of the 

 cellulose consumed by herbivora is, however, broken up by 

 bacteria into acetic and butyric acids, carbonic acid, and 

 marsh- gas. In Man also a small quantity is similarly de- 

 stroyed. 



In the large intestine the bacteric fermentations are not 

 unlike those which occur in the stomach, with, in addition, 

 the destruction of proteins, or of products of proteid digestion. 

 The greater the quantity of undigested food which reaches 

 the large intestine, the greater is the development of bacteria. 

 When the stomach is dilated, the ascending colon, and espe- 

 cially its csecum, is usually dilated also. Bacteric fermenta- 

 tion in the large intestine, with resulting flatulence, is evidence 

 of imperfect digestion, due either to an excess of food or to 

 weakness of the alimentary organs, or, as is more commonly 



