$ear. XXIV. i. 3. AND TEARS. 213 



cretory duets, and a due quantity of faliva is feparated from the 

 biccd* and poured into the mouth ; yet as this maftication of our 

 /ood is always attended with a degree ofpleaiurej and that 

 pleafurab.le fenfatio.u is alio connected with our ideas of certain 

 kinds of aliment ; it follows, that when theie ideas are repro- 

 duced, the pieafurable fenfation arifes along with them, and the 

 falival glands are excited into action, and fill the mouth with fat 

 liva from this fenfitive aflbciation, as is frequently feen in dogs, 

 who Haver at the light of food. 



3. We have alio a voluntary power over the action of thefs 

 falival glands, for we can at any time produce a flow of faliva 

 into our mouth, and f'pit out, or f wallow it at will. 



4. If anv verv acrid material be held in the mouth, as the 

 root of pyrethrum, or the leaves of tobacco, the falival glands are 

 ftimulated into flronger action than is natural, and thence fe r 

 ctete a much larger quantity of faliva \ which is at the fame 

 time more vifcid than in its natural irate ; becaufe the lymphat- 

 ics, that open their mouths into the ducl:s of the falival glands., 

 and on the membranes, which line the mouth, are like wife ftim- 

 ulated into ftronger action, and abforb the more liquid parts of 

 she faliya with greater avidity ; and the remainder is left both in 

 greater quantity and more vifcid. 



The increaied abforption in the mouth by fome ftimulating 

 fubdances, which are called aftringents, as crab-juice, is evident 

 from the inftant drynefs produced in the mouth by a fmaii 

 quantity of tiicrm 



As the extremities of the glands are of exquiiite tenuity, as 

 appears by their difficulty of injection, it was necellary for them 

 tp fecrete their fluids in a very dilute irate ; and, probably for the 

 jmrpofe of ftimulating them into action, a quantity of neutral 

 /alt is likewife fecreted or formed by the gland. This aqueous 

 and faline part of all fecreted fluids is again reabforbed into the 

 habit. More than half of fome fecreted fluids is thus imbibed 

 from the refervoirs, into which they are poured \ as in the urin- 

 ary bladder much more than half of what is fecreted by the kid- 

 neys becomes reabforbed by the lymphatics, which are thickly 

 qifperfed around the neck of the bladder. This feems to be the 

 purpofe of the urinary bladders of hih, as otherwife fuch a re- 

 ceptacle for the urine could have been of no ufe to an animal 

 jmmerfed in water. 



5. The idea of fubdances difagrccably acrid will alio produce 

 a quantity of faliva in the mouth ; as when we fmellvery putrid 

 vapours, we are induced to ipit out our faliva, as if fomething 

 diiagreeable was actually upon our palates. 



<&. When difagreeabic food in the itumach produces naufea„ 



