VOL. XXI.] PHILOSOPHICAL TRANSACTIONS. 405 



saliva did not consist of two juices, whose nature is in such a manner different 

 as to render them apt to ferment on their mixture, it would be very hard to 

 conceive how it should so readily and indifferently serve for the digestion of all 

 eatables ; how it should ferment with, and dissolve so great a variety of things, 

 not only of a different but of a contrary nature ; how it should ferment with 

 acids as well as alkalies, digest things that are cold as well as hot or temperate, 

 &c. But if we suppose that the fermentation which serves for the digestion of 

 the food arises from a peculiar difference in the nature of two juices, which 

 constitute the saliva, it will be easy to give a rational account of our concoction 

 of innumerable things of a different nature. And this seems to be as effectual, 

 and a more certain way to attenuate and dissolve the grosser parts of our food,. 

 than if the fermentation were made only between the saliva and the aliment : 

 besides, the saliva seems to discover a fermentation on the mixture of its con- 

 stituent juices, even at those times when we do not actually eat ; for it is 

 always attended with bubbles, and a froth, when it has not been at all agitated 

 in the mouth ; and many of those bubbles will remain for some considerable 

 time after we have spit it out. 



Nature therefore having appointed the saliva for the digestion of the food, 

 has taken care that it shall be thrown in upon the aliment on every side. Thus^ 

 the glandulae nuckianse and the parotides supply their juices to that part of the 

 food which lies on the outside of the gums, between the cheeks and the teeth, 

 and the glandulae maxillares internas and sublinguales bestow their liquor on 

 the meat which is within the teeth and gums. Nature has also had regard to 

 the mixture of the two different juices of the saliva, which is necessary to its 

 fermentation, by placing the orifices of the salival glands near each other. The 

 saliva being thus mixed, does partly as it is agitated with the food by the teeth 

 and some other parts of the mouth, partly by its own fluidity, insinuate itself 

 into and mix with the food, and not only moisten and soften it, but excite the 

 fermentation which is to dissolve it. And when the aliment is thus mixed 

 with the saliva, which serves to ferment the whole mass, it is then to be con- 

 veyed into the stomach, that great digestive vessel of the body, where it is kept 

 in a digestive heat, and the fermentation not only continued but improved. 

 This fermentation in the stomach first agitates the finer and more subtile parts 

 of the food, and puts them into motion, and so with the fermentation of its 

 own, and those alimentary parts, which it first communicates a motion to, im- 

 proved by the heat of the stomach, the saliva must necessarily act on the grosser 

 parts. For the intestine motion, which is excited in the mass, does not give 

 the particles which are fermented tlie same tendency, but what is so various 

 and confused, that they must inevitably strike not only against one another, but 

 against those which are more gross, so as to attenuate them, sometimes by a 



