7(J DIGESTION 



active digestion has ceased the reaction becomes acid to all 

 three indicators. The differences in reaction are always slight, 

 and there is never a great preponderance of either hydroxyl 

 or hydrogen ions. 



There is no doubt that the acidity of the gastric juice forms 

 an important check on bacterial activity in the alimentary 

 tract, separating the bacteria-infested regions of the mouth 

 and pharynx from the small intestine. But even under normal 

 conditions some active microorganisms of various kinds can 

 be obtained from the stomach. Bacteria which form acid 

 products are less affected by the acid gastric juice than the 

 putrefactive bacteria which are accustomed to an alkaline 

 medium. Normal guinea-pigs fed with cholera bacilli were 

 unaffected. But if the gastric juice was neutralized before 

 administration of the bacilli the guinea-pigs died. By some 

 the bactericidal action of the stomach is considered its chief 

 function, and stress has been laid upon the fact that the stomach 

 in both dogs and man has been removed, leaving, after years, 

 every other organ in perfect health. But it has also been 

 shown that dogs without stomachs might be fed on putrid 

 meat with no harmful effects greater than in a normal dog. 

 So that if an animal can get along without the digestive func- 

 tions of the stomach, it can, likewise, get along without the 

 bactericidal action of the stomach contents. 



QUESTIONS ON CHAPTER III 



Define a foodstuff. 



Give classification of foodstuffs and describe each group. 



Discuss enzymes; define and give general properties. 



Discuss manner of action of enzymes. 



What reason is there for the belief that enzymes act by hydrolysis? 



In what sense may oxygen be called a food? 



Describe the saliva. What is its composition? 



What is the function of saliva? 



Give detailed steps of the action of ptyalin on starch. 



What is the action of acid on the activity of ptyalin? 



Why is starch more easily digested when cooked than when raw? 



Describe the gastric juice. 



What are the proofs that the acid of the gastric juice is free hydrochloric 

 acid? 



How is the reaction of the blood and the urine affected during active 

 secretion of gastric juice? 



What is pepsin? 



Give detailed steps of the action of hydrochloric acid and pepsin on 

 proteins. 



