SALIVARY DIGESTION 57 



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 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 contents are thoroughly mixed with 

 the acid gastric juice and the consequent 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 considerable period of time, and in this region during 

 that time salivary digestion may proceed undisturbed. 



It has been found that salivary amylase acts more efficiently when 

 the saliva is diluted from 4 to 7 times. 1 



Water softened by lime 2 inhibits the action of salivary amylase due 

 to the presence of magnesium hydroxide in this water. 3 Electrolytes 

 have an important influence upon the action of amylases. The Cl ion 

 has a pronounced facilitating action (see Pancreatic Amylase). 



The question of the adaptation of the salivary secretion to diet is one 

 which has received considerable attention in recent years. It has been 

 claimed, on the basis of experimental evidence, 4 that the continued 

 feeding of a carbohydrate diet causes the secretion of a saliva which 

 contains a higher concentration of salivary amylase and one which is 

 therefore able to more efficiently digest the carbohydrate fed. On the 

 other hand, strong evidence 5 has been submitted that the amylase con- 

 tent of the saliva is not increased through the continued feeding of a 

 carbohydrate diet. In general the consensus of opinion is opposed 

 to the adaptation of digestive secretions to diet. 



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

 The principal function of maltase is the splitting of maltose into glucose. 

 Besides occurring in the saliva it is also present in the pancreatic and 

 intestinal juices. For experimental 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. 



It is claimed that the saliva contains dipeptide- and tripeptide- 

 splitting enzymes. 6 Leucyl-glycyl-alanine was the tripeptide split, 



1 Bergeim and Hawk: Jour. Am. Chem. Soc., 35, 461, 1913. 



2 Prepared by treating tap water with one-sixth its volume of saturated lime water, 

 allowing to stand 24 hours and filtering. 



3 Bergeim and Hawk: Jour. Am. Chem. Soc., 35, 1049, 1913. 

 4 NeilsonandTerry: American Journal of Physiology, 15,406, 1905; Neilson and Lewis: 



Journal of Biological Chemistry, 4, 501, 1908. 



6 Mendel: American Journal of the Medical Sciences, Oct., 1909; Mendel and Underbill: 

 Journal of Biological Chemistry, 3, 135, 1907; Mendel, Chapman and Blood: Medical 

 Record, Aug. 27, 1910. 



6 Koelker: Zeitschrift fur physiol. Chem., 76, 27, 1911. 



