AMONG the many interesting features of the human body there are few things of more interest than the process of digestion. Our bodies might well be compared to a steam-engine, the process of making steam answering to the digestive process, one object of which is to produce life or power. The lips may be compared with the door, the mouth with the fire-box, the tongue with the grate, and the stomach and intestines with the flues and their reservoir. At different points along the digestive tract are what might be termed reservoirs; in medical language known as glands. These glands supply a watery fluid peculiar to each, just as the reservoir supplies the engine with water. Later on we will notice the glands and their juices more particularly.
Just as in making steam the different parts of the engine have their work, so in making and sustaining life in man the different organs have their special work. As the fuel door opens, so the lips act. They measure the size of each mouthful.
The month, which we have compared to the fire-box, contains the tongue, the teeth, and the saliva, which is manufactured by three sets of glands. In the mouth food undergoes chemical changes just as fuel does in the fire-box.
Now, the tongue in man, like the grate in the engine, separates objectionable substances and moves the food about so that the teeth may masticate it, and allow the saliva to come in contact with each particle, as the air comes in contact with the fuel when the grate is moved. The next organ is the stomach, corresponding to the tank or reservoir of the engine. Here the food, after it has been partially digested by mastication, is received ; here it undergoes a process of digestion, and is passed on for further action by the intestines. In the lining of the stomach are multitudes of little openings from which ooze gastric juice. These openings with their little pockets are known as peptic glands. Gastric juice contains three digestive substances, pepsin, rennin, and hydrochloric acid. The walls of the stomach, like the entire digestive tract, consist of thin layers of muscle, which contract and relax, thus changing its size and shape. This causes a churning motion, that mixes the gastric juice with the food; and a propulsive movement, which gradually forces the food along toward the intestines.
Below the stomach in the alimentary canal are the intestines, which in their long tubular shape might be compared to the flues of an engine. Here the food is received to be acted upon by the bile, and the pancreatic and intestinal juices.
Food, or the fuel of the human engine, is an item of great importance; for what a person eats, and the way he eats it, determines many of his actions. If irritating or highly seasoned foods are eaten, he is educated to desire something stronger, such as tobacco and liquors. These strong, irritating substances lead to irritability, carelessness, theft, drunkenness, and murder. Then, even when a perfect dietary is used, if the food is not properly masticated, irritation is set up along the alimentary canal, causing the person to do many evil things that he otherwise would not do. "When the stomach is irritated, the excitement is conveyed to the brain through the nerves." And when the brain is out of balance from the injury received by sympathy with the digestive tract, we can see how it is possible for us to do wrong things.
God has made everything to balance exactly. Man has produced scales or balances which are so accurately adjusted that they will indicate the amount of lead used in writing a person's name, but they cannot compare with the nicety of the balance God has created in the universe. It is written, ''Who hath measured the waters in the hollow of his hand, and meted out heaven with a span, and comprehended the dust of the earth in a measure, and weighed the mountains in scales, and the hills in a balance?" Isa. 40:12. God has done all this. He has even comprehended the dust of which we are made. Each one of our members is balanced exactly. There is never any friction unless caused by ourselves. The Spirit of God has said: "To keep the body in a healthy condition, in order that all parts of the living machinery may work harmoniously and in order [or in balance], should be the study of our life." (Christian Temperance p. 53.) As before stated, at different points along the digestive tract are what we have called reservoirs, or glands. In these glands is secreted a fluid peculiar to each one. There are five digestive fluids - viz.: (1) Saliva,- the active principle of which is ptyalin; (2) Gastric juice, in which there are three digestive substances, pepsin, rennin, and hydrochloric acid; (3) Bile, which is alkaline in nature; (4) Pancreatic juice, containing amylopsin, trypsin, steapsiir and a milk-curdling ferment; (5) Intestinal juicer which is alkaline in nature.
In contrast to these fluids there are four food substances; viz.: (1) carbohydrates, which includes starches and sugars, and is the most abundant of all food substances; (2) Proteids, found in the white of egg, lean meat, casein, of milk, and in large proportions in peas, beans, and lentils; (3) Fats which are found in both animal and vegetable foods; (4) Inorganic salts and water. When a portion of animal or vegetable food is burned, an ash is formed, which contains these inorganic salts. Water is found in all food substances.