2i 4 OF THE SALIVA SECT. XXIV. i. 7 . 



a flow of faliva is excited in the mouth by aflbciation ; as efforts 

 to vomit are frequently produced by difagreeable drugs in the 

 mouth by the fame kind of afTociation. 



7. A preternatural flow of faliva is likewife fometimes occa- 

 fioned by a difeafe of the voluntary power ; for if we think about 

 our faliva, and determine not to fwallow it, or not to fpit it out, 

 an exertion is produced by the will, and more faliva is fecreted 

 againft our wi(h ; that is, by our averfion, which bears the fame 

 analogy to defire, as pain does to pleafure ; as they are only 

 modifications of the fame difpofition of the fenforium. See 

 ClafsIV. 3. 2. i. 



8. The quantity of faliva may alfo be increafed beyond what 

 is natural, by the catenation of the motions of thefe glands with 

 other motions, or fenfations, as by an extraneous body in the 

 ear ; of which I have known an inftance ; or by the application 

 of ftizolobium, filiqua hirfuta, cowhage, to the feat of the paro- 

 tis, as ibmc writers have affirmed. 



II. i. The lacrymal gland drinks up a certain fluid from the 

 circumfluent blood, and pours it on the ball of the eye, on the 

 upper part of the external corner of the eyelids. Though it may 

 perhaps be ftimulated into the performance of its natural action 

 by the blood, which furrounds its origin, or by fome part of that 

 heterogeneous fluid ; yet as the tears fecreted by this gland are 

 more wanted at fome times than at others, its fecretion is varia- 

 ble, like that of the faliva above mentioned, and is chiefly pro- 

 duced when its excretory du6l is ftimulated ; for in our common 

 fleep there feems to be little or no fecretion of tears , though 

 they are occafionally produced by our fenfations in dreams. 



Thus when any extraneous material on the eye-ball, or the 

 drynefs of the external covering of it, or the coldnefs of the air, 

 or the acrimony of fome vapours, as of onions, flimulates the 

 excretory duct of the lacrymal gland, it difcharges its contents 

 upon the ball ; a quicker fecretion takes place in the gland, and 

 abundant tears fucceed, to moiften, clean, and lubricate the eye, 



Thefe by frequent nictitation are diffufed over the whole ball, 

 and as the external angle of the eye in winking is clofed fooner 

 than the internal angle, the tears are gradually driven forwards, 

 and downwards from the lacrymal gland to the punclalacryma- 

 lia. 



2. The lacrymal feck, with its punfta lacrymalia, and its nafal 

 duel, is a complete gland ; and is (angular in this refpecl, that it 

 neither derives its fluid from, nor difgorges it into the circulation. 

 The fimplicity of the ftrufture of this gland, and both the ex- 

 tremities of it being on the furface of the body, makes it well 

 worthy our minuter obfervation; as the actions of more intricate 



and 



