SALIVARY DIGESTION 55 



possesses the property of transforming complex carbohydrates such as 

 starch and dextrin into simpler bodies. The action of salivary amylase 

 is one of hydrolysis and through this action a series of simpler bodies are 

 formed from the complex starch. The first product of the action of the 

 ptyalin of the saliva upon starch paste is soluble starch (amidulin) and its 

 formation is indicated by the disappearance of the-opalescence of the 

 starch solution. This body resembles true starch in giving a blue color 

 with iodine. Next follows the formation, in succession, of a series of 

 dextrins, called erythro-dextrin, a-achroo-dextrin, fi-achroo-dextrin, and 

 y-achroo-dextrin, the erythro-dextrin being formed directly from soluble 

 starch and later being itself transformed into a-achroo-dextrin from which 

 in turn are produced fi-achroo-dextrin, y-achroo-dextrin and perhaps other 

 dextrins. Accompanying each dextrin a small amount of maltose is 

 formed, the quantity of maltose growing gradually larger as the proc- 

 ess of transformation progresses. (Erythro-dextrin gives a red color 

 with iodine, the other dextrins give no color.) The next stage is the 

 transformation of the final dextrin into maltose, the latter being the prin- 

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

 a small amount of glucose is formed from the maltose through the ac- 

 tion of the enzyme maltase. The above changes may be represented 



graphically as follows: 1 



Starch 



I 

 Soluble starch 



I I 



Erythro-dextrin Maltose 



' I I 



a-Achroo-dextrin Maltose 



I 



I I 



j3-Achroo-dextrin Maltose 



7-Achroo-dextrin Maltose 



Maltose 



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

 tions. It will act in the presence of relatively strong combined HC1 (see 

 page 139), whereas a trace (0.003 per cent to 0.0006 per cent) of ordinary 

 free hydrochloric acid will not only prevent the action but will destroy 

 1 For a recent discussion of starch digestion see Blake: Jour. Am. Chem. Soc., 38, I245i 

 1916539, 3i 



