The gastric juice is a clear, colorless fluid with strongly acid reaction. It contains.5 per cent, of solids, its specific gravity being 1002. The amount secreted in the day is extremely variable, and depends upon the quantity and character of the food; in well-fed dogs it has been estimated to be one-tenth of the body weight.

It contains: -

1. About.2 per cent, of free hydrochloric acid in man, but in the dog considerably more. The lactic, formic, butyric, and other acids which have been found in the gastric juice probably depend on the decomposition of some of the ingesta.

2. Pepsin, the specific substance which gives the gastric juice its digestive qualities, is a nitrogenous ferment which, with the foregoing acid, acts on proteids. About.3 per cent, is present in the secretion of the human stomach.

3. Associated with the pepsin are other less-known ferments, one of which curdles milk without the presence of any acid.

4. A variable quantity of mucus is found in the secretion of the stomach.

5. It contains.2 per cent, of inorganic salts, chiefly chlorides of sodium, potassium and calcium.