The intestines or guts, are a continuation of the stomach, they are a canal which is generally reckoned six times as long as the subject it is taken from; it is distinguished in small tenuia, and wide crassa.
Each again is divided into three parts: the tenuia, or small narrow intestines, are the duodenum, or twelve finger-gut; the jejunum; the ileum: The wide or crassa, is divided into the cæcum; the colon; and the rectum.
Throughout the whole canal of intestines are numbers of little vessels, called lacteals, which lead the chyle, extracted from the aliment, into a receptacle, which is lodged in the mesentery, and from thence, by another duct call’d the thoracic duct, is carried along the back-bone upwards, and joins to the left subclavian vein, where the chyle gradually commences to be blood.
This short description we will let suffice, and now enter upon the action itself.
The morsel now, which is designed for food, is taken into the mouth, masticated with the teeth, turned about with the tongue; and as the mouth is at work, the saliva or spittle is squeezed from the salival glands, and thus intermixed with the aliment; when enough chewed and moistened with this saliva, it is conveyed to the pharynx, or swallow, which receives it, and, by its contraction, forces it into the oesophagus; and by a repeated contraction, is carried down into the stomach.
There it is again moistened with saponaceous liquid, or pancreatic juice; by which and by a perpetual motion of the stomach, it is brought into a state of digestion; then by small degrees entered through the pylorus or porter, into the first division of the gut, the duodenum.
This gut is about twelve fingers long; and whilst the aliment is there, it is intermixed with the gall, which is a liquor separated by the liver, and contained in the gall bladder; this liquor, the gall, is carried into the duodenum, by a small duct, called the ductus cysticus; where also enters another kind of liquor called the pancreatic juice.
When the aliment is thus prepared, and fit for a particular state of dissolution, it is carried into, and through the jejunum. This gut is in length about twelve or thirteen hands breadth, and its motion somewhat brisk; through which the aliment passes pretty quick, and hence, generally is somewhat empty.
As it passes through this part, the chyle is separated from it by the lacteals, which are small vessels that separate the chyle from the aliment, and abound there more than in any other part of the gut.
From thence it comes into the ileum; that is the longest of all the divisions of the guts, and is in length about twenty-one hands breadth; it has a great many circumvolutions, and next to the jejunum, has many lacteals to separate the chyle.