The stomach forms a part of the digestive tract, and in order to understand its functions thoroughly, it will be best to give a short review of the entire process of digestion. By the term "digestion" are understood all processes which serve to convert the various bod-stuffs into such a condition that they become fit or entrance into the circulation. These changes are effected by means of ferments, which replace the Bmsen flame of the chemist in the laboratory of the iving organism. The ferments are produced by living cells, and possess certain properties in the way of effecting chemical changes when in contact with certain substances. All these changes can ultimately be explained as an hydration of anhydrides - i.e., the substances developed by their presence contain more water than the primary substances.

All ferments possess the six following qualities:

1. They are of organic nature.

2. They act only in the presence of water.

3. The total amount of the formed products contains more hydrogen and oxygen (in the relation of water) than the original substance.

4. They decompose peroxide of hydrogen.

5. They act best at temperatures varying between 30° and 60° C.

6. Each ferment possesses a specific action, and one and the same substance may develop different products when in contact with different ferments.

The ferments are divided into two classes:

1. Formed ferments: those whose active principle cannot be separated from the original cell in which they are generated and is dependent on the life of their mother substance (yeast cells).

2. Unformed ferments: those which can be separated from their original soil without losing their specific action.

Most of the ferments that exist in the living organism are unformed (ptyalin, pepsin, rennet, trypsin, etc.).

Thus far all attempts to isolate ferments in a chemically pure state have been unsuccessful. We only know that they are organic bodies whose structure is similar to that of the proteids.

In the mouth the food first comes in contact with the saliva by the act of chewing. This secretion consists of the products of the salivary and mucous glands of the mouth. It is of alkaline reaction, low specific gravity (1.002-1.009), contains epithelia, mucus, ptyalin, albumin, and some salts. It also contains traces of potassium rhodanate (CNKS). After being lubricated by the saliva, the food passes through the pharynx and oesophagus into the stomach. The ptyalin, which is characterized by converting starch into maltose or sugar, begins its action upon the food already in the mouth, but the principal work is done during the first period of digestion within the stomach.