PROPERTIES AND COMPOSITION OF THE SALIVA 173 



mixed with the salivary secretions ; and that from the posterior part 

 of the tongue, the tonsils, and the pharyngeal glands passes down to 

 the stomach with the alimentary bolus. 



Mixed Saliva. Although the study of the distinct secretions dis- 

 charged into the mouth possesses considerable physiological importance, 

 it is only the liquid resulting from their mixture that can properly be 

 considered in connection with the general process of insalivation. On 

 the introduction of food, the quantity of saliva is increased ; and the 

 influence of the sight, odor and occasionally even the thought of 

 agreeable articles has already been mentioned. 



Quantity of Saliva. It is not easy to estimate in the human 

 subject the entire quantity of saliva secreted in the twenty-four hours; 

 and considerable variations in this regard exist in different persons and 

 in the same individual at different times. An approximate estimate 

 may be arrived at by noting as nearly as possible the average quantity 

 secreted during the intervals of digestion and adding to it the quantity 

 absorbed by articles of food. The following represents the quantities 

 of saliva secreted during mastication and during the intervals of meals 

 (Dalton):- 



Saliva during mastication . . . . .17.32 ounces (491 grams). 



Saliva secreted in intervals of mastication . . 27.93 ounces (792 grams). 



Total quantity per day . . . .45.25 ounces (1283 grams). 



The total daily quantity of saliva, therefore, is a little more than two 

 and three-fourths pounds. 



General Properties and Composition of the Saliva. The mixed 

 saliva taken from the mouth is colorless, somewhat opaline, frothy and 

 slightly viscid. It has a faint and somewhat disagreeable odor soon 

 after its discharge. If allowed to stand, it deposits a whitish sediment, 

 composed mainly of desquamated epithelial scales with a few leuco- 

 cytes, leaving the supernatant fluid nearly clear. Its specific gravity 

 is variable, ranging between 1004 or 1006 and 1008. Its reaction is 

 almost constantly alkaline ; although, under certain abnormal conditions, 

 it has been found neutral, and sometimes, though rarely, acid. It 

 becomes slightly opalescent by boiling or on the addition of strong 

 acids ; and the addition of absolute alcohol produces an abundant 

 whitish flocculent precipitate. Almost invariably the mixed saliva 

 presents a more or less intense blood-red tint on the addition of a per- 

 salt of iron, which is due to the presence of a sulphocyanate either of 

 potassium or of sodium. 



A number of analyses of the human mixed saliva have been made 

 by different chemists, presenting, however, few differences, except in 



