"Other Uses of the Digestive Fluids.—In addition to the uses which we have already stated, several of the digestive fluids possess other interesting properties. The saliva aids the stomach by stimulating its glands to make gastric juice. The gastric juice and the bile are excellent antiseptics, by which the food is preserved from fermentation while undergoing digestion. The bile also stimulates the movements of the intestines by which the food is moved along, and aids absorption. It is remarkable and interesting that a fluid so useful as the bile should be at the same time composed of waste matters which are being removed from the body. This is an illustration of the wonderful economy shown by nature in her operations.
"The food is moved along the alimentary canal, from the stomach downward, by successive contractions of the muscular walls of the intestines, known as peristaltic movements, which occur with great regularity during digestion.
"Absorption.—The absorption of the food begins as soon as any portion has been digested. Even in the mouth and the esophagus a small amount is absorbed. The entire mucous membrane lining the digestive canal is furnished with a rich supply of blood-vessels, by which the greater part of the digestive food is absorbed.
"Liver Digestion.—The liver as well as the stomach is a digestive organ, and in a double sense. It not only secretes a digestive fluid, the bile, but it acts upon the food brought to it by the portal vein, and regulates the supply of digested food to the general system. It converts a large share of the grape-sugar and partially digested starch brought to it into a kind of liver starch, termed glycogen, which it stores up in its tissues. During the interval between the meals, the liver gradually redigests the glycogen, reconverting it into sugar, and thus supplying it to the blood in small quantities, instead of allowing the entire amount formed in digestion to enter the circulation at once. If too large an amount of sugar entered the system at once, it would be unable to use it all, and would be compelled to get rid of a considerable portion through the kidneys. The liver also completes the digestion of albumen and other food elements."
Time Required for Digestion.—The length of time required for stomach digestion varies with different food substances. The following table shows the time necessary for the stomach digestion of some of the more commonly used foods:—
| hrs | min | |
| Rice | 1 | 00 |
| Sago | 1 | 45 |
| Tapioca | 2 | 00 |
| Barley | 2 | 00 |
| Beans, pod, boiled | 2 | 30 |
| Bread, wheaten | 3 | 30 |
| Bread, corn | 3 | 15 |
| Apples, sour and raw | 2 | 00 |
| Apples, sweet and raw | 1 | 30 |
| Parsnips, boiled | 2 | 30 |
| Beets, boiled | 3 | 45 |
| Potatoes, Irish, boiled | 3 | 30 |
| Potatoes, Irish, baked | 2 | 30 |
| Cabbage, raw | 2 | 30 |
| Cabbage, boiled | 4 | 30 |
| Milk, boiled | 2 | 00 |
| Milk, raw | 2 | 15 |
| Eggs, hard boiled | 3 | 30 |
| Eggs, soft boiled | 3 | 00 |
| Eggs, fried | 3 | 30 |
| Eggs, raw | 2 | 00 |
| Eggs, whipped | 1 | 30 |
| Salmon, salted, boiled | 4 | 00 |
| Oysters, raw | 2 | 55 |
| Oysters, stewed | 3 | 30 |
| Beef, lean, rare roasted | 3 | 00 |
| Beefsteak, boiled | 3 | 00 |
| Beef, lean, fried | 4 | 00 |
| Beef, salted, boiled | 4 | 15 |
| Pork, roasted | 5 | 15 |
| Pork, salted, fried | 4 | 15 |
| Mutton, roasted | 3 | 15 |
| Mutton, broiled | 3 | 00 |
| Veal, broiled | 4 | 00 |
| Veal, fried | 4 | 30 |
| Fowls, boiled | 4 | 00 |
| Duck, roasted | 4 | 30 |
| Butter, melted | 3 | 30 |
| Cheese | 3 | 30 |
| Soup, marrowbone | 4 | 15 |
| Soup, bean | 3 | 00 |
| Soup, mutton | 3 | 30 |
| Chicken, boiled | 3 | 00 |
The time required for the digestion of food also depends upon the condition under which the food is eaten. Healthy stomach digestion requires at least five hours for its completion, and the stomach should have an hour for rest before another meal. If fresh food is taken before that which preceded it is digested, the portion of food remaining in the stomach is likely to undergo fermentation, thus rendering the whole mass of food unfit for the nutrition of the body, besides fostering various disturbances of digestion. It has been shown by recent observations that the length of time required for food to pass through the entire digestive process to which it is subjected in the mouth, stomach, and small intestines, is from twelve to fourteen hours.
Hygiene of Digestion.—With the stomach and other digestive organs in a state of perfect health, one is entirely unconscious of their existence, save when of feeling of hunger calls attention to the fact that food is required, or satiety warns us that a sufficient amount or too much has been eaten. Perfect digestion can only be maintained by careful observance of the rules of health in regard to habits of eating.
On the subject of Hygiene of Digestion, we again quote a few paragraphs from Dr. Kellogg's work on Physiology, in which is given a concise summary of the more important points relating to this:—