DIGESTION 355 



We are not without other examples of digestive juices destined to 

 act in a medium with an opposite reaction to their own. The ' saliva* 

 of Octopus macropus, strongly acid though it is, contains a proteo^ 

 lytic ferment which in vitro acts, like trypsin, better in an alkaline 

 than in an acid solution. The pepsin of the (in itself) alkaline secre- 

 tion of the pyloric end of the stomach becomes a constituent of the 

 acid gastric juice ; and it may, perhaps, be considered a morphia* 

 logical accident, so to speak, that the oxyntic cells of the cardiac end 

 should mingle their acid products with the (presumedly) alkalinq 

 secretion of the chief cells in the lumen of each gland-tube, instead 

 of being massed as a separate organ with a special duct. 



In the lower portions of the small intestine bacteria of 

 various kinds are present and active ; and it is not unlikely 

 that even throughout its whole length a certain range of 

 action is permitted to them, checked by the acidity of the 

 chyme, though scarcely by the antiseptic properties of the 

 bile. The stomach, with its acid contents, forms during the 

 greater part of gastric digestion a valve or trap to cut off the 

 upper end of the intestine from the bacteria-infested regions 

 of the mouth and pharynx, and to destroy or inhibit the 

 micro-organisms swallowed with the food and saliva. The 

 occasional presence in vomited matter of sarcinae or regu- 

 larly arranged groups of micrococci, generally four to a 

 group, shows that under abnormal conditions the gastric; 

 contents are not perfectly aseptic ; and even from a normal 

 stomach active micro-organisms of various kinds can be 

 obtained. But upon the whole there is no doubt that th 

 acidity of the gastric juice is an important check on bacterial 

 activity during the first part of digestion, and in the upper 

 portion of the alimentary canal. 



And, indeed, Koch has shown that the acidity of the gastric 

 juice of a guinea-pig is sufficient to kill the comma bacillus 

 of cholera. Normal guinea-pigs fed with cholera bacilli were 

 unaffected. But if the gastric juice was neutralized by an 

 alkali before the administration of the bacilli the guinea-pigs 

 died. Charrin found, too, that digestion with pepsin and 

 hydrochloric acid causes an appreciable destruction or at- 

 tenuation of diphtheria toxine. Naturally, bacteria, like thq 

 lactic acid bacillus, which form acid products are less affected 

 by the acid gastric juice than the putrefactive bacteria, which, 

 on the whole, form alkalies, and are therefore accustomed to 

 an alkaline medium. 



