260 DIGESTION. 



Composition of Saliva. 



Water 994 'io 



Solids . . . . . . 5-90- 



Ptyalin 1-41 



Fat 0-07 



Epithelium and Mucus . . 2 '13, 



Salts : 



Sulpho-Cyanide of Potassium . 

 Phosphate of Soda 



,, ,, Lime . . . 



Magnesia . . ( 2 



Chloride of Sodium . . . 

 ,, ,, Potassium . 



5 '90 



The rate at which saliva is secreted is subject to consider- 

 able variation. When the tongue and muscles concerned! 

 in mastication are at rest, and the nerves of the mouth 

 are subject to no unusual stimulus, the quantity secreted is 

 not more than sufficient, with the mucus, to keep the mouth 

 moist. But the flow is much accelerated when the move- 

 ments of mastication take place, and especially when they 

 are combined with the presence of food in the mouth. It 

 may be excited also, even when the mouth is at rest, by 

 the mental impressions produced by the sight or thought 

 of food ; also by the introduction of food into the stomach. 

 The influence of the latter circumstance was well shown in 

 a case mentioned by Dr. Gairdner, of a man whose pharynx 

 had been divided : the injection of a meal of broth into 

 the stomach was followed by the secretion of from six to 

 eight ounces of saliva. 



Under these varying circumstances, the quantity of saliva 

 secreted in twenty-four hours varies also ; its average 

 amount is probably from two to three pints in twenty-four 

 hours. In a man who had a fistulous opening of the 

 parotid duct, Mitscherlich found that the quantity of saliva 

 discharged from it during twenty-four hours, was from two 



