Chymifaction, or the transformation of food into chyme, is the next important step in the process of digestion. The food, after mastication, passes into the stomach: here it is formed into a homogeneous mass, partly fluid and partly solid, which is called chyme. What is the exact philosophy of this process has been a matter of some discussion, into which it is not necessary now to enter; nor is it yet satisfactorily settled, so as to admit of any definite instruction being given.

The theory which is now generally received respecting the manner in which the stomach acts upon food, is, that the gastric juice possesses a solvent power by which the food becomes reduced to a uniform mass. The solvent power of the gastric juice is very great in healthy, vigorous stomachs; but varies in strength according to the energy of that organ.

The solvent power of the gastric juice is evidently controlled by the vital principle, or principle of life. While the gastric juice of a healthy stomach acts vigorously upon the hardest kind of food, yet sometimes, when it comes into contact with anything possessed of the principle of life, its power is stayed.

Worms, while living, are not affected by it; but when destroyed, are often digested.

The gastric juice possesses the property also of coagulating liquid albuminous substances. The stomach of the calf is used for this purpose by the dairy women, in making cheese. When the infant throws up its milk because the stomach is too full, that milk will be more or less curdled; and instead of considering this curdling an indication of disease, it should be considered a symptom of a healthy stomach.

The time ordinarily occupied in the process of chymifaction, when food has been properly masticated, has been ascertained to be FOUR OK FIVE HOURS. The first hour of this period is occupied in the process of intermixing the food, after it enters the stomach, with the gastric juice. After this is accomplished, an alternation of contraction and expansion of the stomach, or a kind of churning motion, takes place, and continues till the whole mass is converted into chyme, and is conveyed to the first intestine or duodenum, to undergo another change.