*i 4 OF THE SALIVA Sect. XXIV. i. y 



a flow of faliva is excited in the mouth hy aflbciation ; as effort* 

 to vomit are frequently produced by disagreeable drugs in the 

 mouth by the fame kind of aflbciation. 



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

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

 our faliva, and determine not to f wallow it, or not to fpit it out, 

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

 againit our wifh ; that is, by our averfion, which bears the fame 

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

 modifier-: ions of the fame difpoiition o. r the fenforium. See 

 I ifsIV. 3. 2. 1. 



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

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



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

 eir ; of which I have known an initance ; or by the application 

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

 tis, as fome writers have affirmed. 



II. 1. 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 eyelid . Though it may 

 perhaps be flimulated into the performance of its natural action 

 by the blood, which (unrounds 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 duel is flimulated ; for in our common 

 Step 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 

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

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

 excretory duel: of the lacrymal gland, it difcharges its contents 

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

 abundant tears fucceed, to moiflen, clean, and lubricate the eye. 



Thefe by frequent nictitation are diflfufed 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 puntla lacryma- 

 lia. 



1. The lacrymal facie, with its punct? lacrymalia, and its nafal 

 duc"t, is a complete gland •, and is (insular in this refpecf, that it 

 neither derives its fluid from, nor difror^es it into the circulation. 

 'J he fimplicity of the ftructure ol thi:, gland, and both the ex- 

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

 ■worthy our minuter obfervation \ as the actions of more intricate 



and 



