INSALIVATION. 161 



tain increase in the flow of saliva from a tube introduced 

 into the duct of Steno, on the application of vinegar to the 

 mucous membrane of the mouth ; but this was slight as com- 

 pared with the increase in the flow of the submaxillary secre- 

 tion. 1 There is, in fact, a great difference in different animals 

 as regards the excitability of the salivary glands by substances 

 introduced into the mouth. In the human subject, the exci- 

 tation produced by sapid substances will sometimes induce a 

 great increase in the flow of the parotid saliva. Mitscherlich 

 and Ebeiie 2 observed this in persons suffering from salivary 

 fistula, and noted, furthermore, that the mere sight or odor 

 of food produced the same effect. Magendie mentions a case 

 in which the sight of food produced such an effect that the 

 saliva was discharged from the duct to the distance of several 

 feet. 8 



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 con- 

 ditions 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. 

 It is not rational to suppose that the parotid is an exception 

 to this rule ; and Bernard has shown that galvanization of the 

 small root of the fifth pair of nerves and of the facial immedi- 

 ately produces an intense parotid secretion. 4 The fact that 

 an alternation in the parotid secretion accompanies an alter- 

 nation in the act of mastication is also an argument against 

 this mechanical theory; for it is not to be supposed that 



1 BERNARD, Lecons sur les Proprietes, etc., des Liquides de V Organisme, Paris, 

 1859, tome ii., p. 250 et seq. 



2 MITSCHERLICH, Ueber den Speichel des Menschcn. Poggendorff's Annalen der 

 PhysiTc und Chemie, 1833, Bd. xxvii., S. 328. 



3 MAGENDIE, Freds JEUmentaire de Physiologie, Paris, 1836, tome ii., p. 56. 



4 BERNARD, Lemons de Physiologie Experimentale, Paris, 1856, p. 69. 



11 



