Chapter XIII as to pus pockets, should impress upon both parents and

teachers the fundamental importance of proper care of the teeth. This includes not only the prevention of decay by daily thorough cleaning and the securing at intervals of not more than six months of dental inspection with treatment where necessary, but also in the case of children with deformed jaws the special treatment necessary to bring the teeth into position for effective chewing. Too much stress can scarcely be laid on the importance of these precautions.

The moistening of the food with saliva is likewise important to good digestion. As a matter of fact, without it even the act of swallowing would be impossible. One can easily prove that insufficient moistening prevents swallowing by eating a rather large quantity of a very dry food, like crackers. A common habit of people is to moisten the food with water which they drink instead of waiting for it to be properly moistened by saliva. Contrary to popular belief there is absolutely no objection to drinking water at mealtime. In fact, the presence of the additional liquid in the alimentary tract is probably beneficial rather than the reverse; there is, however, a very serious objection to using water for washing down half-chewed food. The best possible way to judge whether the food is sufficiently chewed is by observing whether it has been sufficiently moistened so that it will be swallowed easily. If so, the chances are that the chewing has been sufficient. Between mouthfuls as much water may be taken as one desires, although if ice water is drunk, it should be held in the mouth until the worst chill is taken off before being swallowed, so that it will not chill the stomach. Since the comfort of drinking ice water is in the cooling of the mouth and throat and not at all in the cooling of the stomach, this increases rather than diminishes the enjoyment one gets from a glass of it on a hot day. So much satisfaction can be obtained by proper drinking habits, that it is a pity to allow the health to be injured by improper habits to such an extent as to necessitate, as frequently happens, the complete abandonment of water drinking with meals.

The saliva is primarily for the purpose of moistening the food, but besides this it is also a definite digestive juice, because it contains one of the digestive enzymes. This enzyme, to which is given the name _ptyalin_, acts upon starch, changing it to sugar, but not to the particular sugar of which the body makes use. Perhaps we should digress for a moment to say that there are chemically a number of sugars. These are in many respects alike, although they also vary a good deal among themselves. For example, some are much sweeter than others; glucose, which is a sugar that can be made from cornstalks and other plant products, is not nearly so sweet as cane or beet sugar, although one is fully equal to the other so far as nutritive value is concerned. Of all the various kinds of sugar that exist, only those in the glucose class can actually be used by the body, so that all other sugars have to be changed by digestion into a glucoselike sugar before passing on into the blood. The enzyme of saliva converts starch not into glucose but into a more complex sugar to which is given the name of maltose. It, therefore, starts digestion, but does not carry it through to completion. Starch digestion begins during the course of chewing and mixing the food with saliva; it goes on while the food is being swallowed, and for a short time after it enters the stomach, being stopped there sooner or later by means which will be described in a moment. No other real digestion occurs in the mouth, although the chewing and moistening are of very great importance in preparing the food for the digestion that is to come further along.

The food that is swallowed passes down the esophagus and enters the stomach. Before speaking of this it will be necessary to recall what was said in Chapter VII about the behavior of the stomach walls. Between meals these are in a relaxed and flabby state, with the opposite walls lying more or less in contact. There is usually a little liquid and some swallowed air in the stomach, so that it is not actually empty, even when we speak of it as being so. Just before mealtime the walls of the stomach draw up so that instead of a flabby bag we have a fairly tense tubular organ. It is at this time that the contractions of the stomach wall, which we recognize as hunger, begin to come on. There is a sphincter muscle between the esophagus and stomach which closes the opening tightly and so prevents the pressure within the stomach from forcing gas or liquid back up into the esophagus. This sphincter opens automatically only in connection with the act of swallowing. Every time we make a swallowing movement a sort of wave passes down the esophagus, and when this wave arrives at the stomach the sphincter relaxes, allowing whatever was moving down the esophagus to enter. If one watches a horse or cow in the act of swallowing, the rather deliberate progress of this wave down the neck can be followed. What happens as we eat a meal is that every mouthful, as it is swallowed, is passed through the sphincter into the stomach and room is made for it by a gradual relaxation of the stomach wall, so that, as we saw in Chapter VII, the pressure of the stomach against its contents stays fairly steady, in spite of the fact that more and more material is being taken into the stomach from the esophagus. One result of this behavior of the stomach is that the first food that is swallowed is nearest to the stomach walls, and that which is swallowed afterward is nearer the middle, being inclosed on all sides by the previously swallowed food. This is fairly important because the gastric juice is secreted by glands in the wall of the stomach and so will get in contact first with the food that is swallowed first, and only afterward will reach the food that was swallowed later. Occasionally the sphincter between the stomach and the esophagus relaxes unexpectedly; this is said to happen more often in smokers than in nonsmokers. The result is that some of the sharply acid stomach contents are forced up into the esophagus and vigorous swallowing is necessary to crowd them back down into the stomach. The burning sensation which accompanies this is known as heartburn, although, as we have just seen, it is really entirely a matter of the esophagus and has nothing whatever to do with the heart.

Although the stomach carries on a certain part of the work of digestion, its primary purpose, as we shall see presently, is to serve as a storage place into which a considerable amount of food can be placed in a few moments and so enable us to do our eating at three or four definite meals instead of little by little throughout the day. When we rise from table after any meal, we have in our stomachs roughly one-third of our total food supply for the day, the exact proportion depending, of course, on our individual habits as regards our distribution of food-taking among the three meals. During the two to four hours following the meal this accumulated material in the stomach will be passed along little by little to the small intestine, which is the real digestive organ of the body. In the course of this time there will be some additional digestion within the stomach, but not enough to prepare any foodstuffs for actual use by the tissues. The outlet from the stomach to the small intestine is guarded by

another sphincter similar to that which closes the opening between the esophagus and stomach. This sphincter is ordinarily closed tightly, relaxing occasionally to let a little food through into the small intestine. It is interesting to note, however, that the sphincter does not hold against some materials; for example, water that is drunk between meals passes rapidly from the stomach on into the small intestine. It is said that raw oysters, raw white of egg, and other materials of a similar consistency also pass the sphincter immediately. Most other kinds of food material cannot pass unless the sphincter actually relaxes.

Shortly after food begins to enter the stomach churning movements are set up. These consist of regular contractions of the smooth muscle beginning at about the middle of the stomach in the form of a ring and so causing a deep depression to form right around the stomach, which then travels along toward the sphincter at the outlet. This, of course, crowds the food up toward that end; but if the sphincter does not relax, the food instead of escaping simply squirts back through the space left in the middle of the ringlike construction and so is actively churned. A regular procession of these waves travels over this part of the stomach during the whole time that gastric digestion is going on. The outer half of the stomach, the side toward the esophagus, does not join in this churning motion. The walls here remain quiet, merely pressing upon the food to crowd it up into the part where the churning is going on as fast as room is made for it there. At intervals during this process the sphincter relaxes and a small mass of food is crowded through into the small intestine; then the sphincter closes again, preventing more from passing until the former mass has had time to be acted upon by the digestive juices in the intestine. The way in which this sphincter is controlled is one of the very interesting facts of physiology, but before describing it we shall have to say something about actual gastric digestion.

The juice which the glands in the stomach wall secrete is called gastric juice. This contains three important constituents, first of which is hydrochloric acid. From the standpoint of chemistry it is a very interesting thing that the gastric glands should he able to manufacture a mineral acid like hydrochloric acid. That they do so, however, is proven by the facts of digestion in everybody. In addition to hydrochloric acid gastric juice contains two enzymes; the first is pepsin, which begins the digestion of protein foods, although it does not carry it through to completion. The other constituent is the enzyme rennin, which clots milk; this property appears to be useful in that clotted milk will not pass the sphincter into the small intestine as quickly as it would if it were liquid, and so the digestive processes can go on in milk after clotting just as it goes on in any other of our foods. Since milk is the chief, and in many cases the only, food of the young it is of course very important that its digestion should be very efficiently carried on. As the food is churned by the stomach muscles, it becomes mixed with gastric juice. Any milk that is present will be clotted and any protein will begin to be digested. The food will also be mixed with hydrochloric acid. It happens that the salivary enzyme, ptyalin, will not act in the presence of an acid, so that as soon as any of the food in the stomach comes in contact with hydrochloric acid of the gastric juice, the digestion of starch by ptyalin stops. Since gastric juice is mixed only with that part of the food which is being churned, the other portion, that in the part of the stomach toward the esophagus, goes right on undergoing salivary digestion. So, contrary to the old idea that salivary digestion is unimportant because there is not time enough during the chewing and swallowing of the food for it to go on effectively, we now know that the latter parts of the meal particularly may be very thoroughly acted upon by ptyalin before the action is stopped through the contact of this part of the food with the acid of the gastric juice.

The sphincter between the stomach and small intestine is operated by hydrochloric acid, making up a remarkably ingenious arrangement for securing the emptying of the stomach as fast as the food is ready to be passed on into the small intestine. In order that gastric digestion may have full opportunity, it is necessary that the food should be thoroughly mixed with the gastric juice. As soon as this has happened, however, it is proper that the food should be passed along to be acted on by the rest of the digestive juices. Until that part of the food which is next to the outlet sphincter is thoroughly mixed with gastric juice there will be no surplus of hydrochloric acid by which to operate the sphincter, but as soon as the mixing is complete there will be a surplus. We have here a simple case of stimulation by a chemical substance; the mere contact of the acid with the part of the sphincter which fronts on the stomach is sufficient to stimulate the smooth muscles in it to relax, and, of course, as soon as relaxation occurs, the pressure of the churning movements upon the food will crowd that part of it which is nearest to the sphincter through into the small intestine.

Now we encounter the second part of the action which is just as interesting as the first part. The small intestine is a rather narrow tube; its cavity is not much more than three-quarters of an inch or so in diameter. If the outlet sphincter from the stomach were to stay relaxed after it once let go, the rapid pressing of the food from the stomach would fill the small intestine quickly to a distance of several feet. It happens, however, that the next of the digestive juices to act upon the food are the pancreatic juice and bile, which are secreted respectively by the pancreas and liver, and are poured into the small intestine by ducts from these organs just a few inches beyond the outlet sphincter from the stomach. In order for these juices to mix well with the food it is important that only a little food come into the small intestine at a time. Otherwise a large part of it would pass the opening of these ducts so quickly that there would be no chance for it to become mixed with the juice from them. What actually happens is that the sphincter relaxes under the stimulus of surplus hydrochloric acid and then as soon as a little food has passed through closes again. The closing as well as the opening is operated by hydrochloric acid, but there is this difference: the opening is the result of the stimulation of acid upon the stomach side of the sphincter; when the same acid comes in contact with the intestinal side of the sphincter, its presence there causes the sphincter to contract. Of course, this means that whenever any food passes out from the stomach into the small intestine the sphincter is stimulated by acid simultaneously from both sides, but under that condition the stimulus which causes the sphincter to contract is more potent than that which causes it to relax, so that whenever there is acid on both sides the sphincter will be shut. The only way in which it can be opened to allow more food to pass out is to get rid of the acid on the intestinal side. This is fairly quickly accomplished, because both the pancreatic juice and bile are strongly alkaline liquids, so that as fast as they mix with the food they tend to neutralize the acid; the result is, of course, that by the time these digestive juices have impregnated the food mass thoroughly and so have accomplished their purpose, the stimulus which keeps the sphincter closed has disappeared and there is left only the stimulus to open it, due to the presence of acid in the stomach. As soon as this condition is reached, the sphincter will open again, another mass of food will pass through bringing its acid with it, which, of course, closes the sphincter promptly, and so the whole story goes on again. This action has been described in detail because it is one of the very best examples we have of the remarkably ingenious arrangements by which the complex bodily functions are carried on automatically.

From what we have just said it is evident that the proper emptying of the stomach and, therefore, the proper carrying on of the whole process of digestion, depends upon the formation and outpouring of ample supplies of acid-containing gastric juice. A failure of gastric secretion is bound to be followed by a failure of the stomach to empty itself. Instead of going on to the small intestine where digestion is completed and the digestion products passed on to the blood stream to be used by the body, the food mass lies inert in the stomach. After a few hours, if not immediately, the acute symptoms of indigestion are certain to develop. We are describing not a theoretical possibility but an actual happening in the life of thousands of people, sometimes almost daily. Indigestion is one of the great causes of misery and of impaired efficiency throughout the civilized world. It is said that Napoleon lost the Battle of Waterloo on account of an acute indigestion which befell him on the morning of the crucial day.

There are several causes of indigestion. Among them should be mentioned food poisoning; that is, the inadvertent taking of some material which instead of being a food proves to be actively poisonous. A second type about which we shall have something to say presently is the result of poisoning by substances which are products of the putrefaction of the intestinal contents. A third type, and the one in which we are particularly interested at this moment, is the one which results from the failure of gastric juice to be properly secreted. A fourth occasional cause of indigestion, which should be mentioned in passing, is that which results from eyestrain, and is avoided by properly fitted glasses. There is comparatively little food poisoning; most persons who are susceptible to poisoning from particular kinds of foods find it out promptly and learn to avoid the article which poisons them. A good deal of indigestion is the direct result of intestinal sluggishness; this usually comes on gradually enough to give warning of its approach. Sharp attacks for which there seems to be no justification are nearly always the result of the failure of gastric secretion. Because of the practical importance of this topic a very large amount of study has been devoted to it, and its story makes one of the very fascinating chapters of physiology.

Our space permits us to touch on it only very lightly. It begins with the time back in the middle of the eighteenth century when a couple of Italian investigators fed sponges inside perforated metal capsules to birds and animals and after recovering and squeezing the sponges demonstrated that the juice which had been soaked up would dissolve meat. The scene then shifts from Italy in the middle of the eighteenth century to our own country at the close of the first quarter of the nineteenth, when a French-Canadian lad, by the name of Alexis St. Martin, was brought in to the frontier army post on Mackinac Island with a gaping gunshot wound in his side. The victim of this accident recovered, but meanwhile a permanent opening into his stomach was left. The army doctor on duty at that post, William Beaumont by name, perceiving the unique opportunity for the study of digestion that was in his hands, employed the young man in his family and for many years studied the digestive process as it went on in his stomach. Next we turn to Russia, where an eminent physiologist, who was still living at last reports, demonstrated by making artificially an opening into the stomach of animals, similar to the one which was made by accident in the case of St. Martin, that the secretion of gastric juice is under the control of the nervous system and, furthermore, that it is under the control of that part of the nervous system which we have already learned regulates the functioning of smooth muscles and glands. Our present knowledge of the nervous system would lead us to expect nothing else, but at the time when these discoveries were made much less was known than now about how the glands, as well as the smooth muscles, are controlled. This Russian investigator showed that it is not necessary for food to enter the stomach in order for gastric juice to be secreted. The enjoyment that accompanies the taking of food into the mouth and so getting its taste and flavor is sufficient to arouse nervous disturbances which excite the gastric glands to activity. On the other hand, unfavorable emotions such as anger, fright, or worry, prevent the discharge of these nervous disturbances and so the glands remain inactive. Hand in hand with this, as we saw in Chapter XII, there will be a complete absence of muscular activity in the stomach; not only does the food fail to be churned, but gastric juice fails to be poured out. No digestion goes on in the stomach nor is the food passed on into the small intestine to be digested there. We can expect nothing else than that indigestion will come on. It appears that in human beings, with their high nervous organization, simple weariness may suffice to hinder the outpouring of the nervous disturbances upon which gastric secretion depends, so that one may not be worried at mealtime, but may be simply overtired and still fail of digesting the food. Fortunately we have means of avoiding this; it has been shown that meat extracts have a definite chemical effect upon the gastric glands, arousing them directly to activity. A hot, well-flavored soup at the beginning of a meal is a great aid to digestion, both because it tends to arouse us to active enjoyment of the meal and also because of the chemical influence it exerts directly upon our gastric glands. Cheerful conversation at table is an aid to digestion, because it contributes to our enjoyment of our food. Heated or angry discussion is to be avoided because of the danger that unfavorable emotional disturbances may be aroused, hampering or even putting a stop to the digestive activities.

We have here a powerful argument in favor of good cookery; some may be inclined to think that food is food and that one kind is about as nourishing as another. Not only theoretically, but in practice, food that is attractive both in appearance and in flavor benefits the body more than unattractive and badly cooked food. Of course, we must recognize that no statement of this sort has absolutely general application. The old proverb which says that “hunger is the best sauce” continues true. Hard-working manual laborers and actively playing children enjoy and digest food that is indifferently attractive. Brain workers and people of moderate health are better for an attractively prepared dietary.

We have now traced the food into the small intestine and will remember that up to this point the actual act of digestion has not gone very far. The enzyme of saliva has decomposed part of the starch, or perhaps all of it, into a complex sugar; the enzyme of gastric juice has split some of the very complex proteins into simpler ones. Of the final products of digestion none has yet been formed; their formation is the work of the small intestine. Into the upper end of it, as we have already seen, pancreatic juice and bile are poured from the pancreas and liver respectively. The pancreatic juice contains three enzymes; one of them is identical with that of saliva and completes the decomposition of any starch that the saliva has failed to act upon; the second is an enzyme which acts upon proteins, differing from pepsin of gastric juice in that it carries the splitting of proteins to completion; the third is the enzyme which acts upon fats. Fats are the most troublesome of all the foodstuffs from the digestive standpoint, because they are insoluble in water. Not only do they themselves offer difficulty, but they smear over the other food masses and make it hard for the digestive juices to get at them. Although the enzyme for digesting fat is secreted by the pancreas, its successful working depends on the presence of bile from the liver. If there is an obstruction of the bile passages, so that bile cannot be poured out into the small intestine, the digestion of fats stops and, along with it to a considerable extent, all the other digestive processes of the intestine. There is a familiar common condition known as jaundice, in which the bile passages become stopped, usually as the result of inflammation. When one is suffering from this condition, it is very important that not much fat be included in the diet; otherwise there is likely to be trouble with indigestion.

In addition to the pancreatic juice and bile there is a secretion known as intestinal juice which is poured out by small glands scattered along the wall of the small intestine. These secrete enzymes which convert the various kinds of sugar into the particular sugar, glucose, which is the one the body can use. The glands also secrete an enzyme which can carry on to completion protein digestion. Thus there is ample insurance that all the foodstuffs shall be made ready for the use of the body.

The next thing in order is for the digested foods to pass from the digestive cavity into the blood. This process is known as absorption. The first part of the alimentary tract from which absorption might occur is the stomach, but, as we have just seen, the process of digestion is not carried far enough in the stomach to fit the foods for going on into the blood stream. Absorption from the stomach is, therefore, undesirable rather than desirable. This is interesting because many condiments, particularly the hot spices and mustard, irritate the stomach lining in such a way as to promote absorption through it. Formerly this was looked upon as an argument in favor of the use of these condiments, but we now realize that it is rather an argument against them. The same applies to alcohol. Alcohol irritates the lining of the stomach and produces absorption through it. Unfortunately for those who desire a physiological argument in favor of the use of alcohol at meals this is a disadvantage rather than an advantage. The great region of absorption is the small intestine, where the digestive process is completed and where, therefore, absorption can properly go on. As to the method of absorption not a great deal needs to be said; there is a very delicate membrane lining the intestine, and just beneath this are the very numerous capillaries through which the blood is flowing; also in the spaces between the capillaries is the tissue fluid which drains into the lymphatic system. The products of protein digestion and glucose pass through the lining membrane of the intestine and through the capillary walls directly into the blood stream and are carried along in it. The digested fats, on the other hand, after passing through the intestinal lining enter the tissue fluids instead of the blood. Incidentally it should be noted that they are rebuilt into tiny fat droplets during the process of absorption, so that what we find in the tissue fluids of the intestine are true fats and not digestion products of fat. These tiny fat droplets pass away from the intestine by way of the lymphatic system. This, as we saw in the last chapter, drains finally through large lymphatic vessels into the great veins just at the entrance of the heart, and so the fat finally reaches the blood stream, but not so directly as do glucose and the digestion products of protein.

There is a reason for this difference in the handling of fats and the other foodstuffs which will be clear when we recall the point made in the last chapter that all the blood which flows through the walls of the intestine is collected in the portal vein and must pass again through the capillaries of the liver before entering the circulation at large. What happens is that all the digestion products, except the fats, pass through the capillaries of the liver, but the fat gets into the blood stream by another way and does not go through the liver en route; for some reason or other it seems to be to the advantage of the body that the fat should not be allowed to circulate through the liver capillaries. It is, as we shall see in a later chapter, a distinct advantage to have the glucose pass through the liver, and there is probably also a good reason for having the digestion products of protein take that course.

The digesting food is moved along the small intestine by contractions of its muscular wall, which travel along slowly in the form of a wave, very much as the wave of swallowing passes down the neck of a cow or horse. These waves do not occur regularly but only now and then; what happens is that several inches or two or three feet of the small intestine will be filled with a food mass which stays for a while at that place, digestion going on in it, and the digested food being absorbed through the wall. Both the digestion and the absorption are aided by a kind of churning motion made up of a series of contractions spaced about an inch apart along the part of the intestine where the food mass lies. These contractions form and disappear quite regularly at the rate of several a minute. They have the effect of squeezing the food mass rhythmically, but do not move it away from the place where it is lying. After this churning has been going on for a while it subsides, leaving that part of the intestine entirely quiet; then a contraction wave sets in at the end of the food mass toward the stomach and pushes the mass bodily along the intestine to a new section where the wave dies out and the churning motion begins again. This process is repeated with every food mass as it comes through from the stomach into the intestine until, finally, usually three or four hours after the first food has commenced to come into the intestine from the stomach, the whole mass has been propelled the length of the small intestine and what is left has been passed on through into the large intestine. The small intestine is about twenty-five feet long in man; flesh-eating animals of about the same size have intestines only about one-half as long; grazing animals the same size, on the other hand, have intestines two or three times longer than those of man; this intermediate length of the human intestine is ordinarily looked upon as indicating that man is adapted to a mixed diet, being neither strictly a flesh-eating nor strictly a vegetable-eating animal.

During the slow passage of the food mass through the small intestine the processes of digestion and absorption are completed, so that very little material enters the large intestine except the indigestible parts of the original food. These are made up mostly of cellulose and similar indigestible vegetable materials, but they include also indigestible fragments of gristle and other meat remnants. It is also worthy of note that the amount of water does not decrease much during the passage of material through the small intestine; in other words the material that enters the large intestine is about as liquid as that which passes from the stomach in to the small intestine. This does not mean that there is no absorption of water from the small intestine; in fact, water that we drink is probably absorbed quite rapidly; what it does mean is that enough water is secreted into the intestine from the blood in the lower parts to keep the whole mass liquid; this is of course important as an aid both to digestion and absorption.

The large intestine, as its name implies, is a tube of much larger diameter than the small; it begins low down on the right-hand side, passes up to about the level of the stomach, then across the body and down on the left-hand side, making thus a sort of inverted “U” in the abdomen; the space within the “U” is filled up by the loops and coils of the small intestine. The first part of the large intestine is devoted to the absorption of water; the result of this absorption is to leave the contents of the large intestine in a semidry condition; absorption of water goes on continuously, so that the longer the material remains in the large bowel, the drier will it become. In the ordinary course of events the material, as it is dried out, is passed along through the large intestine and at intervals, which should not exceed twenty-four hours, the accumulated material is discharged from the body.

Various facts about the functioning of the intestine which have seemed to many people mysterious are easily explained on the basis of what we have next to talk about, which is the presence both in the small and in the large intestine of flourishing colonies of bacteria. It has perhaps not occurred to most of us that we are in the position of involuntary hosts to enormous numbers of these microscopic plants, but that is exactly what we are. There is no possibility of preventing this, since the combination of warmth, moisture, and abundant food, which is afforded within the intestine, is the most favorable possible situation for many kinds of bacteria, and no effort on our part would enable us to be free from them. Fortunately, in the ordinary course of events, we are not affected one way or the other by their presence. In the small intestine their chief diet consists of the sugars which are produced as the result of starch digestion or are eaten directly. In connection with nourishing themselves from these sugars, they bring about what is known as alcoholic fermentation; that is, some of the sugar is converted into alcohol with a by-product of carbon dioxide. Exactly the same thing happens when yeast develops in a mass of dough; in the latter case the bubbles of carbon dioxide are what we are after, since they are what makes the bread light, the alcohol being driven off by the heat of cooking. In the alcoholic fermentation that goes on in our small intestines the carbon dioxide is a waste product and is passed on out of the body, but the alcohol is absorbed and used as fuel. Little has been said thus far about the physiological effects of alcohol. At this point all we care to say is that alcohol can be oxidized by the body tissues with the liberation of energy and so is a perfectly good fuel food. In the minute amounts in which it is absorbed from the small intestine it is utilized completely and there is not the slightest reason to suppose that it has any ill effects whatever. The objections to the use of alcohol, which have led to its abolition as a beverage in this country, depend on certain definite pernicious drug effects which it shows when consumed in any but the smallest amounts, and which destroy the usefulness of what would otherwise be a valuable article of human diet. Fermentation within the small intestine ordinarily goes on entirely unperceived by us. Certain foods, or the invasion of the intestinal tract by certain species of bacteria, may change the fermentation in such a way that irritating substances are produced which cause the movements of the small intestine to be very greatly increased; its contents are swept on through in very much less than the usual time and we have the condition known as diarrhea.

Within the large intestine bacterial action goes on fully as vigorously as in the small, and because of the smaller relative amounts of digestible food and of water a much larger proportion of the intestinal contents consists of the bodies of the bacteria and of the products of their metabolism. Since the sugars have been completely absorbed out by the time the food reaches the large intestine and the remaining materials upon which the bacteria can feed are more largely of the protein class, the bacterial action changes from fermentation to that which we commonly describe as putrefaction. This type of action, instead of giving rise to alcohol and carbon dioxide, produces a number of highly offensive compounds; many of these can pass through the lining membrane of the large intestine into the blood and so can circulate around the body. Of late years we have realized that these products of intestinal putrefaction are highly poisonous, especially if present in the blood stream in any considerable amount. The term “auto-intoxication,” which we run across frequently in health literature, means strictly the poisoning of the body by the products of intestinal putrefaction. Of course, the condition is much aggravated if putrefaction is allowed to go on for too long a time. The ill feelings which result from constipation and which in the life of very many people constitute a really serious impairment of health are the direct result of poisoning by these putrefaction products. The obvious remedy is the avoidance of intestinal sluggishness; unfortunately this is easier in theory than it often is in practice. Probably two conditions of modern life are chiefly responsible: the first is our tendency to make the diet more and more highly concentrated; that is, to leave out of it more and more the indigestible parts. The result is that not enough indigestible material enters the large intestine to make a sufficient bulk upon which the intestinal muscle can work in moving the mass forward. While bulk is accumulating, both absorption of water and putrefaction are going on, until by the time a sufficient mass is present, it is so dry that the muscles are not able to move it along and it has produced undue quantities of poisons. Obviously the way to treat this condition is by eating more indigestible material. For this purpose there is nothing better than apples in their season. The old proverb “An apple a day keeps the doctor away” has very sound common sense back of it. Apples are not ideal for this purpose for all people, since they frequently cause a distressing evolution of gas or even headache. Nearly everybody, though, by experimenting, can find a time of day at which an apple can be eaten without any digestive trouble whatever, and frequently with considerable benefit. Apples are valuable simply for their bulk of indigestible substance. The process of cooking converts most of this into digestible material, so that for this particular purpose they must be eaten raw. There are various other fruits such as figs, prunes, and raisins which function similarly and in addition have a direct stimulating effect upon the intestinal movements and so favor the discharge of material. Some people can eat popcorn to good advantage, although others suffer from gas distress if they do so.

The second condition of modern life which favors intestinal sluggishness is the sedentary habit which so many of us, both men and women, have. A vigorous outdoor existence is practically never complicated by auto-intoxication. Anyone who can maintain habits of active exercise will usually find himself troubled little by this condition. One further point should be made, and this can scarcely be over-emphasized, since it probably has as much to do as any other single factor in the avoidance of auto-intoxication; this is the development of regular habits in the matter of evacuation of the bowel. It is a general fact of the operation of smooth muscle that it readily develops certain habits. We have already seen an example of this in the behavior of the stomach in connection with mealtime. As we have noted, the stomach lies flabby between meals and enters into a state of tension just about the time that we are in the habit of eating. This adjustment is made no matter what particular habits individuals may have. Those who habitually eat only two meals a day will have this tightening of the stomach twice a day; others whose habit it is to eat five times a day will have a similar tightening five times in the twenty-four hours. Similarly the large intestine can establish a regular habit with regard to evacuation. This is best done in childhood, so that parents by insisting upon regularity in their children in this respect can usually assure them of a lifetime in which there will be little trouble from auto-intoxication. On the other hand, parents who are neglectful of their children’s welfare in this respect are laying up for them a lifetime of trouble and very much discomfort.

In concluding this part of our discussion we should note that artificial stimulation to intestinal activity should be regarded as a measure of last resort and under no circumstances as a habitual means of inducing evacuation. Persons who allow themselves to become dependent upon laxatives are laying up for themselves trouble, since these invariably become less and less effective, making it necessary to increase the dose and finally establishing a condition in which only the vigorous efforts of a physician will restore the body to normal. A safe general rule is that anyone who finds himself becoming dependent upon laxatives should immediately put himself under competent medical care for the purpose of restoring his system to normal functioning in which he will not be dependent upon drugs.