n6 



BIOLOGICAL CHEMISTRY 



DIGESTION IN THE MAMMAL 

 Digestion in the Mouth 



The first stage of digestion occurs in the mouth, where the 

 food is mixed with the secretions of the salivary glands. In 

 some animals (dog for instance) these secretions are merely 

 lubricating but in others the secretions contain an enzyme 

 called ptyalin or salivary amylase. The amylase has the 

 power of converting the polysaccharides, cooked starch, 

 glycogen and dextrin into simpler carbohydrates. 



The changes that take place in the hydrolysis of starch are 

 indicated in the following table : 



TABLE XX 



Glycogen undergoes a similar series of changes, passing from glycogen to 

 erythrodextrin, etc. 



Although the above represents the general outline of 

 carbohydrate hydrolysis, we must remember that it is possible 

 to isolate several erythrodextrins and several achroodextrins, 

 depending on the ease with which they are precipitated by 

 salts or by alcohol. In the actual hydrolysis ah 1 these sub- 

 stances occur in the mixture. It seems probable that the 

 enzyme splits off one molecule of maltose from the starch and 

 then a second molecule, so that one can represent the hydrolysis 

 as taking place in a series of stages as follows.* 

 Starch 



Soluble Starch 



tose 



* H. T. Brown and J. Heron, Jour*. Chem. Soc., 1877, T. vol. 35, 

 P- 596, and C. O'Sullivan, ibid., p. 770. 



