This section is from the book "Animal Physiology: The Structure And Functions Of The Human Body", by John Cleland. Also available from Amazon: Animal Physiology, the Structure and Functions of the Human Body.
52. The food is received into the digestive or alimentary tube; there it is subjected to a series of agencies by which it is in greater or less part digested or reduced to a condition in which it can be sucked up by appropriate vessels; and, while this portion is absorbed into the circulation, the effete remainder passes on and is discharged. The digestive tube, beginning at the mouth, is continued to the stomach by the throat and gullet, while the stomach is succeeded by the small and great intestine. In its passage along this tract, the food is subjected to both mechanical and chemical processes; and it is proposed to follow its course, and mark the mechanical actions to which it is subjected, before directing attention to the chemical changes. But, among the first of these mechanical actions is that of the teeth; and the whole structure and history of these may be conveniently considered at the outset, previous to noticing their action in mastication.