SALIVARY DIGESTION. 55 



blue color with iodine. Next follows the formation, in succession, 

 of a series of dextrins, called erythro-dextrin, a-achroo^-dextrin, 

 ft-achroo-dextrin and y-achroo-dextrin, the erythro-dextrin being 

 formed directly from soluble starch and later being itself trans- 

 formed into a-achroo-dextrin from which in turn are produced /?- 

 achroo-dextrin and y-achroo-dextrin. Accompanying each dextrin 

 a small amount of iso-maltose is formed, the quantity of iso-mal- 

 tose growing gradually larger as the process of transformation pro- 

 gresses. (Erythro-dextrin gives a red color with iodine, the other 

 dextrins give no color.) The next stage is the transformation of 

 the y-achroo-dextrin into iso-maltose and subsequently the transfor- 

 mation of the iso-maltose into maltose, the latter being the princi- 

 pal end-product of the salivary digestion of starch. At this point 

 a small amount of dextrose is formed from the maltose, through 

 the action of the enzyme maltase. 



Salivary amylase acts in alkaline, neutral or combined acid solu- 

 tions. It will act in the presence of relatively strong combined 

 HC1 (see page 119), whereas a trace (0.003 P^ 1 " cent to 0.006 per 

 cent) of ordinary free hydrochloric acid will not only prevent the 

 action but will destroy the enzyme. By sufficiently increasing the 

 alkalinity of the saliva to litmus, the action of the salivary amylase 

 is inhibited. It has recently been shown by Cannon, that salivary 

 digestion may proceed for a considerable period after the food 

 reaches the stomach, owing to the slowness with which the con- 

 tents are thoroughly mixed with the acid gastric juice and the conse- 

 quent tardy destruction of the enzyme. Food in the pyloric end 

 of the stomach is soon mixed with the gastric secretion but food in 

 the cardiac end is not mixed with the acid gastric juice for a con- 



tsiderable period of time and in this region during that time sali- 

 vary digestion may proceed undisturbed. 

 Maltase, sometimes called glucase, is the second enzyme of the 

 saliva. It is an amylolytic enzyme whose principal function is the 

 splitting of maltose into dextrose. Besides occurring in the saliva 

 it is also present in the pancreatic and intestinal juices. For experi- 

 mental purposes the enzyme is ordinarily prepared from corn. 

 The principles of the " reversibility " of enzyme action were first 

 demonstrated in connection with maltase by Croft Hill. 



Microscopical examination of the saliva reveals salivary corpus- 

 cles, bacteria, food debris, epithelial cells, mucus and fungi. In 

 certain pathological conditions of the mouth, pus cells and blood cor- 

 puscles may be found in the saliva. 



