27. This very considerable waste of the body is repaired by the aliment taken into the stomach. In the mouth it is mixed with a considerable quantity of the liquid called _saliva_, and in the stomach with another called the _gastric juice_, with which that organ always abounds. From the stomach it passes into the intestines, where it is mixed with other two fluids; one called the _pancreatic juice_, the other the _bile_. This last is of a yellow colour, and is sometimes produced in enormous quantities, insomuch that Dr. Wade, in his account of the fevers in Bengal, mentions some patients who have voided by stool half a gallon of bilious matter in one day. 28. In the stomach principally the aliment undergoes a certain change called _digestion_, by which it becomes capable of being converted into the substance of the body. Much has been inquired and disputed, to no purpose, about the nature of this change, and how it is effected. One party has declared for _attrition_; a second for _putrefaction_; a third for _heat_; a fourth have supposed that our meat was digested by _chewing_; as if, like the lobster, people had teeth in their stomach! and, lastly, some learned moderns, after much pains and trouble, have found out that it is digested by _solution_. Dr. Moore has summed up the discoveries concerning digestion in the following words: “The food, being previously divided and blended with the saliva and air by mastication, (chewing) is swallowed, and meets in the stomach with the gastric juice, whose dissolving power, assisted by the natural heat of the place, is the principal agent in digestion. The process is completed by the pancreatic juice and bile, the nutritious parts of the food being by this process converted into chyle for the support of the body, and the grosser parts thrown out.”[53] [53] Moore’s Medical Sketches. 29. The inside of the stomach and intestines are full of the mouths of innumerable small vessels, which continually suck up from the aliment, as it passes downwards, the finer parts, in form of a white liquid, called _chyle_; and from the whiteness of their colour the vessels have the name of _lacteals_, from the Latin word _lac_, milk. After passing through the substance of the stomach and intestines, and running along the membrane called the _mesentery_, to which the intestines are attached, the lacteals unite in a large reservoir called the _thoracic duct_; and this again opens into a large vein on the left side, called the _subclavian_, which conveys the blood from half the upper part of the body; soon after terminating in the vena cava, by which the chyle is conveyed to the heart, thence to the lungs, and so on in the common course of circulation. The conversion of the chyle into blood is called the process of _sanguification_.