166 PHYSIOLOGY OF ALIMENTATION. 



tion of the fatty constituents of the food by certain bacteria 

 which are killed when the secretions from the gastric mucous 

 membrane are normal, in part through the action of the 

 lipase normally present in the gastric secretion, which in 

 the absence of hydrochloric acid can exhibit its character- 

 istic activity. 



Throughout the duodenum, jejunum, and ileum bacteria 

 are exceedingly scarce, dependent also it seems upon a 

 deleterious action of the secretions of these portions of the 

 alimentary tract upon the bacteria. It is entirely probable 

 that the scant bacterial development found in these locali- 

 ties is determined chiefly by the fact that the alimentary 

 contents are neutral or faintly acid in reaction. The pres- 

 ence of even traces of free acids inhibits the growth of most 

 bacteria very markedly. It must be remembered also that 

 the food passes through the small intestine fairly rapidly, 

 so that little time is allowed for bacterial growth. 



The pancreatic juice does not seem to have any bac- 

 tericidal action. DUCLAUX found bacteria as constant inhab- 

 itants of the pancreatic duct, where they are bathed in the 

 secretions from the gland. They also develop readily on 

 macerated pancreas. It is of interest after what has been 

 said above that the pancreatic juice is alkaline in reaction. 



Nor has the bile any great antiseptic action, for accord- 

 ing to TALMA even but slightly virulent colon bacilli can 

 produce a severe inflammation of the liver when injected 

 into the gall-bladder. Whether the pancreatic and biliary 

 secretions together, or these in conjunction with the intestinal 

 juice, have a bactericidal action is not yet determined. 



In the large intestine, beginning with the caecum, the 

 number of bacteria increases enormously to reach, by the 

 time the rectum is reached, the gigantic proportions which 

 have been discussed above. The cause of the prolific develop- 

 ment of micro-organisms in the large intestine is by no means 

 clear. The fact that the intestinal contents assume an 

 alkaline reaction after the ileocsecal valve is passed no 



