SALIVA. 



207 



the horse, the organic matter passed through .a mixture of sulphate of soda but was 

 coagulated by sulphate of magnesia. Almost all physiologists agree that this organic 

 matter is not identical in its properties with albumen or' with the peculiar principle 

 described by Miahle in the mixed saliva, under the name of animal diastase. 



A compound of sulpho-cyanogen is now generally acknowledged to be a constant 

 constituent of the parotid saliva. This cannot be recognized by the ordinary tests in the 

 fresh saliva taken from the duct of Steno, but in the clear, filtered fluid which passes 

 after the precipitation of the organic matter, there is always a distinct red color on the 

 addition of the persulphate of iron. As this reaction is more marked in the mixed saliva,, 

 the methods by which the presence of a sulpho-cyanide is to be demonstrated will be 

 considered in connection with that fluid. 



In the human subject, the parotid secretion is more abundant than that of any other 

 of the salivary glands. The entire quantity in the twenty-four hours has not been 

 directly estimated ; but Prof. Dalton found that, during mastication, the quantity secreted 

 in twenty minutes on one side was 127'5 grains, and on the other side, 374'4 grains. 



A curious fact with regard to the influence of mastication upon the flow from the 

 parotids was observed by Colin in the horse, ass, and ox. He found that, when mastica- 

 tion was performed on one side of the mouth, the flow from the gland on that side was 

 greatly increased, exceeding by several times the quantity produced upon the opposite 

 side. This fact was confirmed by Dalton, as already indicated, in the human subject. 



The flow of saliva from the parotid takes place with greatly-increased activity during 

 the process of mastication. The orifice of the parotid duct is so situated that the fluid is 

 poured directly upon the mass of food as it is undergoing trituration by the teeth ; and, 

 as the secretion is more abundant on the side on which mastication is going on, and the 

 consistence of the fluid is such as to enable it to mix readily with the food, the function 

 of this gland is supposed to be particularly connected with mastication. This is undoubt- 

 edly the fact ; although its flow is not absolutely confined to the period of mastication, 

 but continues, in small quantity, during the intervals. Its quantity is regulated some- 

 what by the character of the food, being much greater when the articles taken into the 

 mouth are dry than when they contain considerable moisture. There is a great difference 

 in different animals as regards the stimulation of the salivary glands by substances intro- 

 duced into the mouth. In the human subject, the stimulus produced by sapid sub- 

 stances will sometimes induce a great increase in the flow of the parotid saliva. Mits- 

 cherlich and Eberle observed this in persons suffering from salivary fistula and noted, 

 furthermore, that the mere sight or odor of food produced the same effect. 



The supposition, which has been entertained by some authors, that the flow from the 

 parotid is dependent upon the mechanical pressure of the muscles or of the condyle of 

 the lower jaw during mastication has no foundation in fact. It is now well established 

 that one of the indispensable conditions in the production of a secretion is a great increase 

 in the quantity of blood circulating in the gland, and that the vascular supply is regulated 

 through the nervous system. The fact that an alternation in the parotid secretion accom- 

 panies an alternation in the act of mastication is also an argument against this mechanical 

 theory ; for it is not to be supposed that during mastication there exists a difference in 

 the pressure of the muscles or of the condyles on the two sides, corresponding with the 

 differences which have been noted in the secretion from the glands on either side. In 

 the horse and in the dog, it has been observed that the secretion of the parotids is com- 

 pletely arrested during the deglutition of liquids, while the flow from the other salivary 

 glands is not affected. 



To sum up the functions of the parotid saliva aside from any chemical action which 

 it may have upon the food, which will be fully considered in connection with the mixed 

 saliva it evidently has an important mechanical office. It is discharged in large quan- 

 tity during the entire process of mastication and is poured into the mouth in such a 

 manner as to become of necessity thoroughly incorporated with the food. Its function 



