Now the aliment comes into the wide gut, and gradually becomes fæces; and first, the cæcum: This part is rather an appendix only, and hangs from the main part like a finger to a glove. The use of this gut has been much controverted by anatomists; it seems however, very probable, that this appendix is designed to keep the aliment in for further digestion, as it now begins to putrefy, and becomes fæces or excrement.
From thence it enters the colon, which is a long, and very winding intestine; it runs up along and about the liver, touches the gall bladder, and the spleen; from thence it descends again to the os sacrum. It has but few lacteals, and is, as it were, the last drainer of the fæces: It is this intestine which is the seat of the Colic, and of most other complaints of the belly.
Next to this comes the last and straightest, the rectum; this gut is closely adherent to the sacrum, and ends in the fundament; which is provided with muscles to open and shut the anus, in order to contain the fæces, and discharge it.
The mechanism of chylifaction in the human body differs from the brute creation in general, except that most contemptible of the whole, the hog; to which it bears a very near resemblance, insomuch that there is very little distinction.
Both have that advantage over the generality of terrestrial animals, that they are confined to no particular food; which favours greatly the luxury of the one, and the beastiality of the other.
The brute creation are generally distinguished into carnivorous and granivorous: The first is that kind which feeds upon flesh; and the latter upon grain and vegetables. Upon examination however, we find, that the stomach and guts are peculiarly adapted to their food; and that grass agrees no more with the dog, than mutton does with the horse.
But man is so happily made, that any thing which is food, is proper for him, and he may become used to it; and thus is either carnivorous or granivorous.
The whole canals, from the stomach to the anus, is in a continual vermicular motion, which is called the peristaltic motion; by this the aliments are dissolved, and disunited; and as they pass along, are drained by the lacteals, of their nutriment or chyle.
These lacteals are, by means of a membrane (with which they are surprisingly interwoven, and connected to the whole canal) called the mesentery, lead regularly into one common cistern, lodged almost in the middle of the intestines, in that membrane, called the receptacle of chyle; and from thence the chyle is carried by a duct up along the back-bone, called the ductus thoracicus, into the left subclavian vein, where it gradually commences to be blood.
By this mechanism we are nourished, and the substance of our food converted into blood, and transported through the whole animal machine, for the support of every part of its wonderful composition.