[6]. An opinion has lately been broached, that the lymphatics are all absorbing vessels, of the same nature with the lacteals, and that they all join to empty themselves in the subclavian vein to the common mass of the blood; but this to me, seems too general, and contradicts experience.
From hence we see plainly how these three organs, the brains, the lungs, and the heart, are concerned, and mutually assist each other in the actions, and circulation of the fluid of life; nothing could move without the sensation of the nerves; these could not exist without the blood, from which they receive their support; the blood could not circulate without the heart, arteries, and veins; and in them it could not move with a necessary freedom, except its being supplied with a sufficiency of air from the lungs: So that evidently all three are so interested in this grand movement, that the stopping of the one, must needs be the stopping of the whole.
SECT. VI.
Of Chylifaction and Nutrition.
In the preceding we have briefly considered the state of the fluid of life, and mechanical instruments of their motion in the human machine. In this we will consider how the whole is supported, and the vital lamp, from time to time, becomes supplied.
Under this consideration we will examine the canal of food, and the various changes the morsel undergoes from the time we take it in our mouths, till the nutriment is reduced to blood, and the remaining dross is expelled the body as useless.
The animal functions towards chylifaction and nutrition, are mastication, or chewing the food; deglutition, or swallowing; digestion; chylifaction; nutrition; and the excretion of the fæces.
In order therefore to understand this clearly, it becomes necessary to describe the organs which nature has formed for the requisite performances thereof.
In the first place then, smelling is that sensation which nature has given to every animal, that has a choice of food, as the first safe-guard to inform it of any thing agreeable or disagreeable, useful or pernicious to its body; its seat is in the nose chiefly, but we find by experience, that it has a friendly connection with our palate and stomach; for the effluvia of any thing will either create a desire, or give us the greatest aversion to every substance that throws out a flavour.