[Sidenote: Action of gastric juice on fat]
The gastric juice does not act on fat, but in the case of animal food, in which the membranes or connective tissues that enclose the fat-cells are formed of proteid material, the gastric juice sets the fat-globules free by dissolving these enclosing membranes.
The chief action of hydrochloric acid in the stomach is to aid the action of the pepsin. Pepsin alone has no digestive power. There are no other acids produced by the secretive glands of the stomach. If other acids are found in the contents of the stomach, it is because they have been taken in with the food, or produced by abnormal fermentation.
[Sidenote: How hydrochloric acid is formed]
The source of hydrochloric acid is from the sodium chlorid or common salt of the blood. The secreting cells of the stomach-glands are thought to have the power to form hydrochloric acid by uniting the chlorin of the salt with the hydrogen of the water. This is a very unusual chemical process, and has not yet been successfully produced in a laboratory.
[Sidenote: Hydrochloric acid as an antiseptic]
One of the chief functions of hydrochloric acid in the stomach is that of an antiseptic. In other words, hydrochloric acid kills bacteria. This is not true of all bacteria, for some germs can live in an acid medium, while others may live best in an alkaline solution. The alternation of the digestive juices from alkali to acid is a provision of Nature which has a dual purpose:
1 To reduce food to the finest possible solution; that is, to subdivide or to digest food elements into a form that will admit of assimilation and use
2 To destroy bacteria and enzyms of plant and animal origin that are taken into the digestive tract with food
(These two facts constitute additional reasons for the thorough mastication of food)
[Sidenote: Object of alternating digestive juices]
By such plan Nature provides for the digestion of food only by such enzyms and ferments as will produce a finished product wholly suited to the particular requirements of the body. When we attempt by artificial processes to digest our food with other enzyms than those of our own digestive organs, or take into the stomach large quantities of food without proper mastication, which causes fermentation, we may expect that the nutritive material supplied to our tissues will not be perfectly adapted to the needs of human cell-growth, and, as a natural result, consequent derangement of the body-functions will take place.