Food and Digestion.
From the earliest dawn of existence to the last moment of life, our bodies are constantly changing. Old particles of matter, when they are worn out, leave their places and are thrown out of the system. Were this the whole of the matter, our bodies would soon waste away, and that would be the end of us. But as fast as the old materials are thrown away, new ones take their places; and it is solely out of our food that these new materials are formed.
In order that the food may be well digested, it must first be broken into small particles in the mouth. The act of chewing it is called mastication. During this act, if it be well performed, a large quantity of spittle, called saliva, flows out of a number of glands, called salivary glands, and mixes with the food, forming with it a soft mass. In this condition, it is thrown backward into the top of the throat, called the pharynx. Here, a little cartilage, called the epiglottis, drops down upon the opening into the top of the windpipe, and prevents its entrance into the breathpassage; and it is pushed along into the gullet, a tube which runs down behind the windpipe and lungs, and which physicians call the esophagus. Here a succession of muscular bands, circular in shape, contract upon it, one after another, and force it down into the stomach.
It is important that two things should be secured while the food is in the mouth, namely, that it should be reduced to a good degree of fineness by chewing, and that a proper amount of saliva should be mixed with it. If the chewing were not necessary, teeth would not have been given us; and the salivary glands would certainly not have been put in the mouth, if the mixing of water with our food would serve the purposes of digestion as well.
Eating too Rapidly. Americans have fallen into a pernicious error in eating their food too rapidly. Time is not given to chew it sufficiently to excite a full flow of saliva; and as it cannot be swallowed in a dry state, it is not uncommon to see persons taking a sip of water after every second mouthful, to enable them to force it into the stomach. It is a habit we Americans have of cheating ourselves both of the pleasures and the benefits of eating; for the only real pleasure of eating arises from the flavor of food while retained in the mouth, and the only benefit we can derive comes in consequence of its proper digestion.
The food when received into the stomach is in the same condition as when taken into the mouth, except that it is, or should be, ground fine by the, teeth, and well mixed with saliva.
The Gastric Juice. The stomach, like the mouth, the windpipe, and the gullet, is lined by a mucous membrane. The chief office of this membrane is to secrete, or take out of the blood, a fluid which we call gastric juice, which means stomach juice, from the Greek name of stomach, yarep (gaster). This fluid has not much smell or taste, and looks like spring water. It has a powerful effect upon food, which, when mixed with it, soon undergoes an important change, which is apparent to the taste, the smell, and the sight. The nature of the gastric juice and how it produces its effect upon food are not certainly known; but it contains two active elements, a free acid and pepsin, whose function is to dissolve the nitrogenous parts of the food and convert them into albuininose or peptone. The albuminose is absorbed by the coats of the stomach and enters directly into the circulation ; while the sugar and fat pass on to the duodenum to be acted upon by the bile, the pancreatic juice, and other secretions of the bowels.
Too Much Cold Water at Meals. There are some interesting facts connected with the formation of this fluid, of which it is important that every person should be apprised.
Its quantity and quality depend on the amount and healthfulness of the blood which flows to the stomach during the first stage of digestion. It is, therefore, injurious to drink large quantities of very cold water with, or immediately after, our meals; as this will chill the stomach, and repel the blood from its vessels, so that but little of the juice can be formed. Digestion, in such case, must be imperfect.
This Fluid not Secreted Without Limit. This fluid does not flow into the stomach continuously, but only when we swallow food, and then not as long as we please to eat, but merely till we have taken what the system requires. If, in the amount we take, we go beyond the wants of nature, there will not be fluid enough formed to dissolve it, and the whole will be imperfectly digested, and be a source of injury rather than benefit. This should teach us to be careful that our food be only reasonable in amount.
Not Secreted in Sickness. When we are sick, the gastric juice is either not formed at all, or only in ,;mall quantities. Whatever may be our feelings of lassitude, and however much we may appear to need food, at such times, it is useless to take it, for it cannot be digested, and will only aggravate our disease. If the illness be only slight, the fluid will be formed to some extent, and food may be taken in proportion.
Its Secretion Favored by Cheerfulness. A cheerful disposition, and a happy, lively frame of mind, are highly favorable to the production of the gastric juice; while melancholy and anger and grief and intense thought of business, at the hour of meals, greatly hinder its natural flow.
This should teach us to go to our meals with light hearts, and to make the family board a place of cheerful conversation, and of a light and joyous play upon the mirthful feelings of all present. Should any of the family circle be in the habit of using vinegar as a concliment, we should never be guilty of compelling them to extract it from our faces. A vinegar face is not easily excused anywhere; at the table it is unpardonable. A single countenance of this description will throw a gloom over a table full of naturally cheerful persons; and if habitually present at the board, may finally spoil the digestion of half a dozen, and entail dyspepsia upon them for life.
The stomachs of the sick pour out but very little of this fluid, and they can take but a small amount of food. It is cruel to deprive them of the power of digesting that little by treating them harshly, and filling them with gloomy and desponding feelings. I therefore repeat the substance of the advice given on a previous page: Deal gently with the sick.
How all this is Known. As the stomach is wholly concealed from view, the reader will very naturally ask bow it is known that the gastric juice is poured into it in certain states of the mind, etc., and withheld in others. It certainly could not have been so accurately known, had it not been for an accident which opened the living and working stomach to the inspection of Dr. Beaumont, a United States Surgeon. A young man by the name of Alexis St. Martin, a Canadian by birth, but then in the State of Michigan, had a large part of his side torn away, and a hole of considerable size made into his stomach, by the accidental discharge of a gun. To the surprise of his surgeon, St. Martin recovered; and the edges of the wound in the stomach refused to grow together, preferring rather to fasten themselves to the borders of the breach in the side, thus leaving the passage open. A kind of curtain grew down over this, which prevented the food from falling out. Dr. Beaumont, taking advantage of this state of things, instituted a series of valuable experiments, by lifting the curtain, and inserting various articles of food, and witnessing the process of digestion.
Movement of the Stomach. The presence of food in the stomach causes its muscular coat to contract and throw it about from side to side, mixing it thoroughly with the gastric juice, and reducing it to a pulpy mass, called chyme. This, as fast as it is properly prepared, passes through the pylorus into the upper bowel, or duodenum, called also the second stomach.
Chyme. A certain witty professor of anatomy and physiology was in the habit of asking his class if they ever saw any chyme; and when they answered, no, as they often did, he called their attention to what is occasionally to be seen in the morning, upon the sidewalks, where drunken men have held themselves up by lampposts, and left the contents of their stomachs.
The pylorus, or opening into the bowel, has a very singular and wise instinct, which is worthy of remark. When a piece of food, which has not been digested, attempts to pass into the bowel, the moment it touches the inner surface of this orifice, it is instantly thrown back by an energetic contraction; though a portion of well prepared chyme, touching the same opening immediately after, is allowed to pass unchallenged.
Chyle. The chyme, when it reaches the duodenum, seems to cause the liver to secrete bile, and the pancreas to produce pancreatic juice. These two fluids are conveyed into the upper portion of the second stomach, and there are mixed with the chyme, and cause it to separate into a delicate, white fluid, called chyle, and a residuum, which, being worthless, is pushed onward, and thrown out of the body.
Bile in the Stomach. Most persons suppose that the bile is generally found in the stomach; but this is a mistake. It is thrown up by vomiting, because in that act, the action both of the first and the second stomach is reversed, and the bile is forced up from the duodenum, taking a direction the opposite of its usual course.
Destination of the Chyle. The chyle being separated from the dregs, is pushed onward in its course by the wormlike motion of the intestine; and as it passes along, it is gradually sucked up by thousands of very small vessels, whose mouths open upon the inner surface of the bowel. These little vessels are called lacteals, from the Latin word lae, which means milk. because they drink this white, milky fluid. Fig. 61 shows a section of the small bowel, turned inside out, and covered with the villi, or rootlike filaments, closely set upon its surface, for absorbing the cbvle, and at the bottom of which the lacteals take their rise.
In these lacteals, and in the mesenteric glands, the chyle is gradually changed, so as to approach nearer and nearer to the nature of the blood ; but precisely what the change is, or how it is effected, is not known. Several learned men have published their theories upon these points, and the writer has opinions upon them; but it is not worth while to trouble the reader with them. It is sufficient to say that the fluid is carried by the lacteals to the thoracic duct, through which it is conveyed into a large vein at the lower part of the neck, where it is poured into the blood, and becomes, after going through the lungs and experiencing another and a vital change, the material out of which our bodies are daily and hourly newcreated.
Fig. 62 gives a general idea of the stomach, bowels, etc. : 9, being the stomach; 10, 10, the liver; 1, the gallbladder; 2, the duct which conveys the bile to 4, which is the duodenum; 3, is the pancreas; 5, the esophagus; A, the duodenum; B, the bowels; C, the junction of the small intestines with the colon; D, the appendix vermiformis; E, the ececum ; F, the ascending colon ; G, the transverse colon; H, the descending colon; 1, the sigmoid flexure; J, the rectum.
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