869. Why do we eat food?

Because the atoms of which our bodies are composed are continually changing. Those atoms that have fulfilled the purposes of nature are removed from the system, and, therefore, new matter must be introduced to supply their place.870. Why do we eat animal and vegetable food?

Because their substances are composed of oxygen, hydrogen, carbon, and nitrogen—the four chemical elements of which the human system is formed. They are, therefore, capable of nourishing the body, after undergoing digestion.871. Why do we masticate our food?

Because mastication is the first process towards the digestion of food. Before animal or vegetable substances can nourish us, their condition must be entirely changed, their organic states must be dissolved, and they must become simple matter, in a homogeneous mass, consisting of the four chemical elements necessary to nutrition, and they must again be restored to an organic condition.872. Why does saliva enter the mouth when we are eating?

Because, in addition to the mechanical grinding of the food by the action of the teeth, it is necessary that it should undergo certain chemical modifications to adapt it to our use. There are placed, therefore, in various parts of the body, glands, which secrete peculiar fluids, that have a chemical influence upon the food.

The first of these glands are the salivary glands of the mouth, which pour out a clear watery fluid upon the food we eat, and which fluid has been found to possess a property which contributes to the digestion of food.

The moisture afforded by the salivary secretion is also necessary to enable us to swallow the food.

"And the Lord said unto him, Who hath made man's mouth? or who maketh the dumb, or the seeing, or the blind? have not I the Lord?"—Exodus iv.

873. Why does the salivary juice enter the mouth just at the moment that we are eating?

Because the glands, which are buried in the muscles of the mouth, and which in their form are much like bunches of currants, are always full of salivary secretion. There are nerves which are distributed from the brain to these glands, and when other nerves which belong to the senses of taste, of sight, or of feeling, are excited by the presence of food, a stimulus is imparted to the salivary glands, through the nerves that surround them, their cells collapse, and the juice which they contain is poured out through their stems, or ducts, into the mouth.874. How do we know that impressions imparted to one set of nerves, may be imparted to another set, so as to put any particular organ in action.

Because very frequently the mere sight of rich fruit, or acid substances, will cause the saliva to flow freely. In this case it is evident that the salivary glands could not see or know that such substances were present. An impression must, therefore, be made upon the brain, through the organ of vision, and the desire to taste the substances being awakened, a nervous stimulus is imparted to the glands of the mouth, and they at once commence their action, as if food were present.875. Why does food descend into the stomach?

Because, after the teeth, the tongue, and the muscles of the mouth generally, have rolled the food into a soft bolus, it is conveyed to the back of the mouth, where it is set upon the opening of the throat (oesophagus). It does not then descend through the throat by its own gravity, because the throat is generally in a compressed or collapsed state, like an empty tube; and we know that persons can eat or drink when with their heads downwards. The oesophagus is formed of a number of muscular threads, or rings, and each little thread is like a hand ready to grasp at the morsel that is coming. As soon as the bolus is presented at the top of the throat, these little muscular hands lay hold of it, and transmit it downward, passing it from one to another, until it is conveyed through the long passage, to the door of the stomach, which it enters.

"Remove far from me poverty and lies; give me neither poverty nor riches; feed me with food convenient for me."—Proverbs xxx.

A. The inner coat of the stomach. (The stomach is here represented cut through its length, so that we can see its inside.)

B. The lower extremity of the throat, or oesophagus, through which food enters the stomach.

C. The passage out of the stomach, called the pylorus, where a muscular contraction prevents the escape of undigested food.

D. The duodenum, and the ducts through which the bile and pancreatic juices enter and mingle with our food.876. Why do we not feel the food being transmitted through the throat?

Because the nerves of the body differ in their powers: some are nerves of feeling, some of motion, and others are nerves of the senses. The nerves of feeling are most abundantly distributed to those parts where feeling is most useful and necessary to us. But the faculty of feeling our food undergoing digestion would be no service to us whatever; therefore the nerves of motion are plentifully distributed to the throat and stomach, but very few of the nerves of feeling—just as many as will tell us when we eat anything too hot, or too cold, or that the stomach is out of order.877. Why do we feel uneasy after eating to excess?

Because the stomach is distended, and presses upon the other organs by which it is surrounded.

"Who satisfieth thy mouth with good things; so that thy youth is renewed like the eagles."—Psalm ciii.

878. Why do we feel drowsy after eating heartily?

Because, while the stomach is in action, a great proportion of the blood of the body is drawn towards it, and as the blood is withdrawn from the other parts of the body, they fall into a state of languor.879. Why does blood flow more freely to the stomach during digestion?

Because the energy of an organ is increased by the flow of blood, which supplies the material of which our organs are composed, and in which the vital essence, supporting life, resides.880. Why does excess in eating bring on indigestion?

Because the power of the stomach to digest food is governed by the amount of food required by the system. It seems to be an instinct of the stomach to hold back food which is in excess, and by indications of pain and disturbance to warn its master that excess has been committed.881. Why is food digested in the stomach?

Because it enters the stomach in the form of a paste, produced by the action of the mouth; and directly food enters, the gastric juice, which is formed by glands embedded in the coats of the stomach, trickles down its sides. This is a more powerful solvent than the salivary juice—it is like the same kind of fluid, only much stronger, and it soon turns the food from a rough and crude paste into a greyish cream (chyme). The heat of the stomach assists the operation, and the muscular threads of the coats move the cream along, in the same manner that the muscles of the oesophagus brought down the food.

The cream is passed towards the door which leads outward from the stomach (pylorus); but if, in the midst of the cream, there are any undissolved particles of food, it closes upon them, and they return again to the stomach to be further changed.

"When thou hast eaten and art full, then thou shalt bless the Lord thy God for the good land which he hath given thee."—Deut. viii.

882. Why does indigestion bring on bilious attacks?

Because the liver secretes a fluid to assist in the digestion of food. The liver is a gland—a similar organ to the glands of the mouth—and it forms bile in the same manner that they form the salivary juice. Only the liver is a much larger gland, and a much greater quantity of blood passes through it. The liver pours its secretion into the biliary duct (Fig. 49) to mix with the grey cream as it passes onward, and to further dissolve it. But when the stomach is excited by food which it cannot dissolve, and when the owner of the stomach, disregarding its remonstrances, will persist in over-eating, or in eating things that disagree with the system, then the liver and the stomach sympathise, and the muscular threads, or hands, that prevail all through the alimentary organs, instead of moving onward, move backward, and throw some bile into the stomach to assist to dissolve and remove the excessive or improper food.