VOL. XXI.] PHILOSOPHICAL TUANSACTIONS. 401 



such strong and corroding acid, without being injured in its tone, and labour 

 under great and extraordinary pains. Neither does such a menstruum, though 

 it will digest some things, seem capable of dissolving so great a variety of 

 things as we eat, especially when many of them are of contrary natures. Some 

 will have the menstruum to be a nitro-aereous spirit, subtile, and very pene- 

 trating, and included in its proper vehicle ; which being in its own nature apt 

 to penetrate the mass of the aliment, diffuses itself through the whole, and 

 breaking the cohesion of the most solid parts, dissolves their compages. By 

 others, it is thought to be some saline juice in the stomach, by which the parts 

 of the aliment are divided and dissolved, and those fit fornourishment are vola- 

 tilized. 



Lastly, there are some who suppose the digestion of the food to be per- 

 formed by means of a ferment, which, when mixed with the aliment, excites 

 in the mass an intestine motion ; and the different and contrary motions or 

 tendency of the parts, making some kind of collision, gradually break off par- 

 ticles from the grosser and more solid parts, till they are so attenuated, as to 

 mix more equally with the fluid parts, and with them constitute one soft or 

 chylous substance. But these also differ either as to the nature of this ferment, 

 or the manner in which it is supplied. For some take it to be the remains of 

 the food that was last digested ; which, having lain some time in the stomach 

 after the rest is carried down into the intestines, contracts an acid, or some 

 other quality, and is so altered as to partake of the nature of a leaven. And 

 this leaven being a part of the food which has been already digested, is so soft 

 and liquid as to be capable of mixing with the aliment which is next taken 

 into the stomach, and being agitated with it by the repeated pressures of the 

 diaphragm, liver, and abdominal muscles on the stomach in respiration, dif- 

 fuses itself through the whole mass, and being mixed with it like leaven, or 

 yest added to new wort, &c. puts it into a state of fermentation, and by this fer- 

 mentation, or the expansion of the ferment, and the more subtile parts, which 

 are first put into motion by it, those parts which are more solid, and with which 

 they are intermixed, are rent and divided, and so attenuated as to become a 

 soft and pulpous matter. And although the greatest part of the food, thus 

 broken and concocted, is by the contraction of the fibres of the stomach pressed 

 into the duodenum, yet they do not contract themselves so as to force out all 

 the aliment, but leave between the rugae or folds on the inside of the stomach 

 a sufficient quantity to be a leaven to the next meal; and so on from time to 

 time. 



Some have a notion that this ferment or principle of fermentation is in the 

 aliment itself; which being a congeries of matter, consisting of vaiious parts of 



VOL. IV. 3 F 



