168 DIGESTION. 



ological interest and importance, it is only the fluid resulting 

 from a union of them all, which can properly be considered 

 in connection with the general process of insalivation. In 

 man it is necessary that the cavity of the mouth should be 

 continually moistened, if for nothing else, to keep the parts 

 in a proper condition for phonation. A little reflection will 

 make it apparent that the flow, from some of the glands at 

 least, is constant, and that from time to time a certain quan- 

 tity of saliva is swallowed. This is even more marked in 

 some of the inferior animals, as the ruminants. The dis- 

 charge ol fluid into the mouth, though diminished, is not 

 arrested during sleep. In the review of the different kinds 

 of saliva, it has been seen that the flow from none of the 

 glands is absolutely intermittent ; unless, occasionally, from 

 the parotid, the secreting function of which is most power- 

 fully influenced by the act of mastication and the impres- 

 sion of sapid substances. 



Upon the introduction of food, the quantity of saliva is 

 enormously increased ; and we have already noted the influ- 

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

 agreeable articles. Many persons present a marked increase in 

 the flow of saliva at the sight of a lemon ; and we are all famil- 

 iar, in a general way, with the impressions which bring " wa- 

 ter into the mouth." 1 The experiments of Frerichs on dogs 

 with gastric fistulse, 2 and the observations of Gardner on a 

 patient with a wound in the oesophagus, 3 have demonstrated 

 that the flow of saliva may be excited by the stimulus of 

 food introduced directly into the stomach without passing 



1 COLIN (op. cit. y p. 471) has failed to excite the salivary secretion in the 

 horse by the sight of food ; but the fact with regard to the human subject has 

 been repeatedly noted by physiologists. 



8 FRERICHS, Die Verdauung. WAGNER'S Handworterbuch der Physiologie, 

 Braunschweig, 1846, Bd. ill, S. 759. 



8 GARDNER, Case of a Wound of the Throat in which the Trachea and (Esoph- 

 agus were divided across, and which did not terminate fatally, although the parts 

 have not reunited. Edinburgh Medical and Surgical Journal, 1820, vol. xvi., 

 p. 358. 



