When we examine the skull, found in the Neander valley, of the primitive man who lived so many thousands of years before us, we are at once struck by the colossal size of the jaws. It would appear that these were necessary in the prehistoric man in order that he might be able to break up thoroughly the indigestible raw foods, not previously prepared by cooking, so that they could be of use to his body. The size of the jaws was here undoubtedly adapted to the nature of the food; it was a necessity and a consequence of the feeding upon foods which required much chewing, with the aid of strong jaws.
Whether another such adaptation existed in the length of the intestine, as we see it in herbivorous animals, remains undetermined. The teeth and the skeletons of these primitive human beings have withstood the ravages of time, but not so the softer portions of the body. That such an adaptation of the intestine existed is rendered probable by the fact that the length of the gut varies in animals of the same species, taken quite young and while growing, when some are fed exclusively upon plant food and the others mostly upon meat. This has been shown by the experiments of Babak. The degree of variation may be quite considerable.
The same thing may be observed in humankind. In those who have, since childhood, been fed upon a diet consisting principally of meat, the intestine is shorter than in those who have subsisted upon a vegetarian diet. In the Chinese and Japanese the intestines are one-third longer than in Europeans. The Eskimos, on the other hand, have a very short intestine. The meat-eaters among animals have a very short and muscular intestine, in order to be able to propel the feces onward and to eject them, since they are not of a nature to excite of themselves any great movement in the intestine. In the herbivorous animals this condition is not necessary.
A similar state of adaptation to the physiological processes may be observed during the digestion, in particular in the fact that the gastric juice is secreted in different ways according to the quality of the food. When meat is eaten, for instance, the stomach secretes hydrochloric acid in considerable amount, in order that the connective tissue may be readily dissolved. When bread is eaten a large quantity of pepsin is secreted, since, as we have learned through the experiments of Pawlow, bread requires five times as much pepsin as the albumin of milk, for instance. Bread thus makes great demands upon the gastric digestion, and black bread, furthermore, imposes the same requirements during the process of intestinal digestion. Milk, however, makes the least demands of any food substance, especially certain kinds of milk in which the caseous matter is precipitated in a more finely divided state, or where, as in kefir, it has been partially digested through the action of bacteria.
Food substances having a very pleasant taste may stimulate the secretion of the gastric juice merely by their appearance and sometimes, even, by simply being called to mind. When a dog is shown a sausage, a secretion of saliva may often be observed; in addition to this, however, large quantities of gastric juice are also secreted, but only after about five minutes. These secreted juices are ready to receive and to digest the food about to be taken. They are actually in waiting for it, and when the food is received it still further stimulates by its presence the secretion of these juices. When a roll with dry, brown crust is taken, the crust must be well masticated, the chewing further exciting the secretion of saliva. The saliva has for its object to assist the descent of the food through the alimentary canal, and after a large amount of saliva has been thrown out the food slips down all the more easily. The drier and harder the food substance is, the more saliva will be required, and nature has provided for this, for the saliva under-goes variations in accordance with the nature of the food, becoming more or less fluid, or of a viscid quality. The only requirement is that man should do his part, and thoroughly masticate hard and dry articles of food. The hard, dry crust of a roll is more easily digested than the soft interior portionleaving aside the fact that its starch has been rendered rather more digestible during the process of bakingbecause it is much more carefully masticated, and because a great deal of saliva is secreted during the process. The saliva is here of especial importance, since the ferment it contains, the ptyalin, plays a notable rôle in the digestion of starchy foods, converting, as it does, the starch into sugar, which is the only form in which starch is taken up and used in the body. All starch must be first turned into sugar, for only in this way, in the form of glycogen, can it be carried to the liver and there stored up.
The saliva also has another important function : it acts as an antiseptic upon many injurious substances which are taken into the mouths with our food. We can best observe in dogs that this is really the case. When a dog has a wound, he is constantly licking it. In the laboratories where I have been working, I have often observed that dogs lick the wounds after operations, and, as good comrades, they even perform this function the one for the other. Such wounds never become infected ; severe wounds, such as those caused by the removal .of the entire thyroid gland, healed without infection in a very short time. When dogs are prevented from licking their wounds, or when, on account of the situation of the latter, the dogs cannot reach them, they very readily become infected.
The stomach is protected against poisoning to an even greater degree by the hydrochloric acid. We very frequently ingest, especially while traveling and the temporary guests of unscrupulous landlords, a number of quite injurious substances in foodstuffs which are not fresh and have deteriorated. This can be observed in a marked degree in animals that have no careful guardians watching over them, and must take their nourishment wherever they can find it. Now, if these decomposed food substances do not hurt the animals, and if we are not harmed by game, etc., which already has a decidedly pronounced odor, it is because of the hydrochloric acid contained in the stomach. We can easily convince ourselves of this fact by simple experiments. If we place some pieces of meat in a 4 or 5 per cent. solution of hydrochloric acid, about as it is in the stomach, they can remain there for some days at room temperature or can even be kept for a week or longer, without there being the slightest odor of decomposition. Decayed meat loses its odor after having been for a time in such a solution.
This property of the gastric juice may be lost in certain diseased conditions of the stomach. When, in addition, the motility of the stomach is seriously diminished and the food substances lie in the stomach for a long time, very injurious decomposition takes place.
A sufficiently acid gastric juice may prove very efficacious in protecting us against certain epidemics, e.g., of cholera, by counteracting the causal factor of the same. Of course, the cholera germs are only then destroyed when the food in which they are contained excites the secretion of stomach acids. When a little fruit containing these micro-organisms, or a glass of infected water, has been taken, either of which will excite only a very slight secretion of acid, no active protection can be expected : a sufficient quantity of meat would have to be taken at the same time. When there is danger of cholera uncooked foods should never be taken upon an empty stomach.
In addition to the above-mentioned property, the acid of the gastric juice also possesses another very important one, namely, that of making the digestion of food possible. This duty, however, seems to be less important than the first mentioned, for when the stomach fails the digestion can be accomplished by the intestine. But should the stomach acid fail, then both animals and man would be in constant danger of being poisoned by an unsuitable food substance. For the digestion itself, the acid is indispensable, for it alone is capable of causing the pepsin in the gastric juice to dissolve the albumin. Pepsin is not given off as such by the main cells of the stomach glands, but rather in a preliminary form, as pepsinogen, and it is then converted into pepsin by the hydrochloric acid of the surrounding cells. Gastric digestion can only be performed by the combination of the two. The hydrochloric acid alone might perhaps exert a softening action upon the albumin, e.g., upon fibrin; it can also dissolve the connective tissue of the meat-fibers and the cellulose of vegetables, but it is only in association with pepsin that it can dissolve the albuminous substances, such as meat or hard-boiled eggs, and convert them into peptone, in which form the albumin is taken up in the body. About 25 to 35 per cent. of the albuminous substances which are peptonized in the stomach may be absorbed by the stomach. All the rest goes into the intestine, and there the peptone is very quickly converted into the amino-acids by a ferment, erepsin, discovered by Cohnheim, which is present in the small intestine in the pyloric region, as well as for a short distance lower down.
With the exception of a portion of the peptones, only a very few foodstuffs are absorbed by the stomach. Alcohol is one of those which are, and sugar is also taken up in small quantities. Water is not absorbed by the stomach, but after remaining there for a time passes into the intestine. Very often a pint of water may remain in the stomach for half an hour. When the stomach is diseased, and the peristaltic action is greatly diminished, water may remain in it for a very long time, sometimes two to three hours. In such cases one can hear, upon percussion of the stomach, a “splashing” of the water for quite a long time after it has been taken. Jaworski has shown that, as a rule, hot water disappears from the stomach much more rapidly than cold water.
The temperature of liquid nourishment, in general, and of water or soup, is not without importance for the stomach, and in many persons much harm may be done by either very cold or very hot drinks. Boas states that many stomach troubles are caused by the habitual use of either very hot or very cold drinks. Among Americans, colic occurs very frequently, and this may, perhaps be due to the custom, which I have myself observed during frequent visits in the United States, of serving water with pieces of ice in it at each meal, even during the winter.
The direct action of the food substances upon the mucous membrane of the stomach is also of importance in digestion. We have already mentioned above that the sight or even the thought or recollection of some very tasty article of food will induce a secretion of gastric juice. The digestive process is thus set in motion, and when the food is taken it is at once brought in contact with the digestive fluids. The food, in its turn, acts upon the mucous membrane, and in this way the process of digestion is continued. The action of different kinds of food varies. Among the most stimulating are meat extracts, and for this reason it is indicated to give a good meat soup to persons suffering from loss of appetite, and to those in whom the psychic secretion of gastric juice is diminished owing to a depressed, melancholic condition. Caviar acts in much the same way.
Alcohol has a considerable stimulating effect upon the secretion of the gastric juice; a diluted alcohol, however, is most efficacious. It is to be remembered that the gastric juice thus secreted contains but little ferment, but, on the other hand, an increased amount of hydrochloric acid. Persons suffering from overacidity of the stomach would do much better not to take any alcohol. Very strong alcohol, like poisons in general, stimulates the secretion of the gastric mucus as a sort of protective measure; strong spices, aromatic substances, mustard, etc., also act in this way.
In certain countries it is the custom to take some strong alcoholic drink just before meals; in France the “apéritif,” containing much alcohol, and in Sweden and Denmark “aqua vitae” are thus used. According to the statement made above, this is not a rational procedure, and represents a sort of “box on the ear” for the stomach, which is really only irritated thereby. Often such a method is merely the final resort to renew the digestive functions in those who have, through gluttony, lost the power of normal stimulation of the digestive process. Meat excites the secretion of the gastric juice, which contains much acid; during the digestion peptones are formed, and these, again, further assist the digestion in precisely the same way as does Liebig’s extract. For the digestion of bread an excessive secretion of acid would be injurious, since the digestion of the starches would be thereby arrested; consequently, with a bread diet the stomach secretes a great deal of pepsin, but very little acid. To be sure, an equal amount of the psychic secretion of gastric juice may occur with bread as with meat, but, after a short time, the flow of juice excited by the bread will gradually cease. Meat from which the ex-tractive substances have been removed by boiling causes but a slight secretion of juice.
Water and also milk stimulate the secretion of gastric juice, but the flow induced is relatively slight. Through the intermediary of the pepsin contained in the stomach the casein is precipitated ; the fluid portion of the milk passes into the intestine, like liquids in general, and the albuminous portion is dissolved in from two to three hours. White of egg excites only a very slight secretion of gastric juice, and for this reason raw eggs are not easily digested. In many cases hard-boiled eggs are better digested.
Stimulation of the flow of gastric juice by means of water may be useful in cases where the psychic secretion does not take place owing to a depressed mental condition, as in neurasthenia. It is also to be observed that one may stimulate a failing appetite by the aid of a drink of water, especially of a kind containing carbonic acid, as do many mineral waters. In many cases alcoholic drinks exert even a better effect. In soups, not only the meat extractives contained, but the watery contents as well, have a stimulating effect upon the secretion. One may thus truly say “L’appétit vient en mangeant”The appetite comes as we eat.
Since starchy foods take up but very little acid in the stomach, their digestion being thereby interfered with, it would be rational to forbid such a diet (with much bread, etc.) in the case of persons suffering from overacidity of the stomach. On the other hand, the meat in the diet must be restricted when the stomach does not secrete any acid, as is the case in many instances of chronic catarrh of the stomach. A meat diet, as already stated, requires principally hydrochloric acid ; when this is lacking, a diet consisting of chiefly macaroni, rice, sago, or tapioca should be advised. These substances, even in healthy persons, simply pass through the stomach, and are then digested, first by the pancreas and afterward the intestine, and finally converted into sugar. We, therefore, advise this variety of diet in these cases in order to spare the stomach and leave the work to the intestine.
The hydrochloric acid also greatly influences the length of time that the food remains in the stomach, since it has an especial action upon gastric peristalsis.
The transit of the foodstuffs from the stomach into the intestine is accomplished through the movements of the muscles of the stomach, which, in a way, shake and stir up the gastric contents. When the food partaken of during a meal passes into the cavity of the stomach, the fundus, it forms an agglomerate mass. Its digestion can only take place. as the juices secreted by the glands of the stomach, viz., the hydrochloric acid and the pepsin, act upon it. The muscular movements of the stomach bring about the contact of the digestive juices with the food. When this has lasted for a certain time, and the food is sufficiently prepared, it is pushed toward the outlet, in the direction of the pylorus. In the pyloric antrum the movements become much more energetic; the food is here thoroughly kneaded and compressed, and converted into a finely divided, pulpy mass. In some animals which feed upon hard grains, e.g., turkeys, the musculature of the stomach is capable of exerting pressure sufficient to crack nuts. In the feeding process of mankind, at least at the present time, such very violent action is no longer necessary, but sometimes considerable work is still required of the stomach in order to compress large indigestible masses, which, as a rule, cannot pass into the pylorus if they are at all larger than a plum, for in-stance. If too large they are pushed back, and it sometimes happens that several attempts have to be made before some such indigestible mass can succeed in passing; in the mean time the fluid portions of the food have already been discharged. We may imagine what an effort is required of the stomach muscle in consequence of the carelessness of hasty eaters and gormandizers ! The importance of thoroughly masticating the food thus becomes evident, for which, of course, a good chewing apparatus is a necessity.
The work of the gastric musculature, as above described, is greatly assisted by the hydrochloric acid contained in the stomach. The acid excites the contractions of the muscles, and regulates the opening of the pylorus: when there is a sufficient amount of acid the muscles bring about a contraction of the region of the pylorus, the opening of which is therefore closed. The food can then be sufficiently digested, whereas, if the pylorus should remain open, it might happen that the undigested food would pass through. The more the acid penetrates into the intestine, the longer the pylorus remains closed. It is necessary that the acid contents passing into the intestine be first neutralized by the alkaline fluids of the latter, for otherwise the very important function of intestinal digestion, which only takes place in an alkaline reaction, would be interfered with. When the acid has been sufficiently neutralized, the pylorus opens and allows another portion of the stomach con-tents to pass through. Thus, as we see, this work is accomplished gradually, which has the advantage that the various digestive fluids may act for a long time. When there is a large amount of hydrochloric acid in the stomach, it may happen that the contractions of the muscles become cramp-like. In such cases a fatty diet may prove beneficial. The fat, indeed, acts in a manner opposite to the hydrochloric acid : it stops the peptic digestion and the secretion of gastric juice, and exerts an inhibiting influence upon the musculature of the pyloric region. In overacidity of the stomach it is desirable to prescribe fats, and these best in the form of =skimmed milk or cream, as recommended by H. Strauss. When the fat is given in association with albumin, as, for instance, in fat pork or goose-meat, the fat exerts a restraining influence upon the musculature, while the albumin, through stimulation, causes closure of the pylorus, so that the food remains in the stomach for a longer time, as we will show later in a table showing the periods required for the digestion of various foods.
In addition to the above-described functions of the hydrochloric acid another very important one must be added, viz., the influence of the acid upon the digestive processes taking place in the intestine.
When the hydrochloric acid passes into the intestine with the food from the stomach, it comes into contact with the epithelium of the glands situated in the mucous membrane of the intestine. Here it acts upon a substance called prosecretin, discovered by Bayliss and Starling, and transforms it into secretin. This, again, either through the agency of the circulation by which it is carried to the pancreas or through the nerves, acts upon this gland, causing the secretion of its juice. The latter only acquires its proper activity when the hydrochloric acid has reacted upon a substance, discovered by Paw-low, contained in the intestinal mucous membrane, namely, prokinase, and has transformed it into the active ferment, kinase. Without this substance the pancreatic juice has no influence whatever upon the albumins; as soon, however, as it comes in contact with the latter, digestion takes place very rapidly. Ferments, in general, are peculiar in that they have the power to cause rapid chemical changes, and that a minimum portion of ferment is sufficient to effect such changes in large quantities of other substances. Through the activity of the kinase the primary representative of a substance contained in he pancreatic juice, protrypsin, is transformed into the active substance, trypsin, which then carries on the digestion of albumins to its end-products, the amino-acids.
A very active ferment of this variety, which digests the peptones formed in the stomach further until they become amino-acids, exists in the mucous membrane of the duodenum and the upper intestineit is also found in the mucous membrane of the pyloric region. It was discovered by Cohnheim, and was named by him erepsin.
In addition to the trypsin, two other important ferments are contained in the juice secreted by the pancreas : pancreatin or amylopsin, which converts the carbohydrates into maltose, and also a small portion into sugar,and steapsin, which, how-ever, is only rendered active by the acids contained in the bile and then proceeds to digest the fats. Fats in their usual form cannot be incorporated in the fluids of the body; they must first become liquid, when not naturally so. The solid fat, e.g., that found in the muscular fibers, must first be fluidifiedit must melt, and, the lower the melting point is, the more readily the fat can be made use of. Fats which already contain fluid oils, such as olive oil and other vegetable oils, are easily digested, as is also butter, which easily becomes fluid. On the contrary, fats such as lamb-fat, which only melts at a temperature exceeding 50° C., are digested with difficulty. In fact, all fats the melting point of which is above 40° C. are hard to digest.
Even when the fat has been melted and is fluid, it cannot yet be digested, since it is not soluble in water. It must first be rendered soluble, and this is accomplished solely by the steapsin, a ferment of the pancreas. This ferment splits the fat into glycerin and fatty acids. The glycerin is soluble, and the fatty acid is converted into soapy substances by the salts contained in the bile, together with the alkaline compounds of the intestineamong which is a certain amount of sodium carbonate. These soaps alone are soluble. After the component parts of the fat have been absorbed by the mucous membrane of the intestines, it is again built up from these same constituents, and becomes the body-fat of man or of animals.
The co-operation of the bile is absolutely necessary for the absorption of the fats. When the former is absent, as, for instance, when the orifice of the bile-duct is occluded by gall-stones (jaundice thereby also resulting), the greater part of the fat remains in the intestine without being absorbed. Such patients must not be allowed to take any fats. According to the experiments of Brugsch, 40 per cent. of the fat is found in the feces when the flow of bile is obstructed. When, in addition, the action of the pancreas is also interfered with by a pathological condition, which usually occurs after long-continued gall-stone disease, the loss of fat may amount to 6o per cent. In one case, cited by Umber in his textbook,2 in which there was no outflow of bile or pancreatic juice whatsoever, only a minimal quantity10 per cent.of the fat was absorbed.
Having explained the action of the three ferments which originate in the pancreatic gland, I would like also to mention that the various forms of nourishment act in different ways upon the secretion of the pancreatic fluids. Water, for instance, has an influence, even though rather a slight one, upon the secretion of the pancreatic fluid.
As Pawlow has shown, the pancreatic fluid contains a large amount of those ferments which are most required by and correspond with the food which has been taken. When, for instance, an animal lives exclusively upon meat and fat, the pancreatic ferment which converts the carbohydratesamylopsinwill be lacking, and I question whether a similar condition does not exist in diabetics, who frequently live, in an irrational manner, upon meat and fats alone, to the exclusion of the carbohydrates.
The secretion of the bile is also greatly affected by the nature of the food. A meat diet causes a considerable flow of bile, as do also fats; consequently, fat in large quantity, olive oil for instance, is given in disease of the gallbladder with impacted gallstones and in attacks of colic.
The presence of the bile in the intestine is of the greatest importance for the digestion, since it not only activates the fat-splitting ferment, but causes the two other ferments of the pancreatic gland to act more quickly and powerfully. The bile also exerts an influence upon the propulsion of the contents of the intestine, and its absence is generally followed by constipation. The intestine, of course, also has a movement proper to itself. By wave-like contractions, such as we see in earth-worms, it pushes the contents downward toward the external orifice. In this manner, the ferments of the fluids secreted by the intestinal glands are enabled to exert their full activity, especially the maltase, which completes the conversion of the starches into sugar. The saliva and the secretion of the pancreatic gland do not have as pronounced an effect upon the carbohydrates as the intestinal fluids : they only convert a small portion thereof into sugar, while the rest forms dextrin and maltose; the maltase thereupon acts on the latter and trans-forms them into grape-sugar (dextrose). It is this substance alone which is capable of being taken up into the system to be stored in the liver in the form of glycogen. The starches and their colloid intermediate products cannot be thus taken up. Cane-sugar must also first be split into dextrose and levulose. This is accomplished by invertin, a ferment present in the intestine. In animals, or in persons living upon milk, another ferment is found in the intestinal juice, viz., lactase, which converts the milk-sugar into galactose and dextrose (grape-sugar).
In addition to these ferments, which act upon the carbohydrates, the intestinal juices contain another ferment, already mentioned, erepsin, which acts upon the albumin. In order to bring the ferments present into intimate contact with the con-tents of the intestine, the latter performs a series of pendulum-like movements.
Various kinds of food exert special influences upon the movements of the intestine. Fatty foods, for instance, arrest the gastric and intestinal movements. Very large quantities of fat, however, have a rather irritating effect, like castor oil. A diet of lean meat only slightly excites the movements of the intestines, so that the contents move forward less rapidly, and during this time can be well absorbed. When the contents, on the other hand, include a large amount of residue, as in a vegetable diet, too great an irritating action is exerted upon the intestinal mucous membrane, and the intestine is too rapidly freed of its contents. When this is the case the food, naturally, cannot be well assimilated, and the principal function of the intestine, that of absorbing the food substances and rendering them available for the benefit of the system, is not carried out.
The question of the assimilation of food in the intestine is a very important one, and will be taken up later. I shall simply mention here that when the food has not been sufficiently cooked, is insufficiently masticated, and insufficiently digested by the gastric juice the intestine must alone perform what has been left unaccomplished. It may then readily hap-pen that a portion of the food which should be absorbed is lost.
The development of local diseases is also greatly favored when the intestine is continually required to perform such excessive work. Then, too, the food itself is not always in perfect condition when taken (e.g., unripe fruit).
When we speak of an easily digested food we must differentiate between digestibility in the stomach and digestibility in the intestine. Calves’ brains, for instance, are readily digested in the stomach, whereas in the intestine 43 per cent. thereof, which cannot be digested, is lost, as has been shown by Rubner. On the other hand, a hard-boiled egg is less perfectly digested by the stomach than by the intestine; the latter succeeds much better with the hard egg than the stomach. Many food sub-stances are digested with difficulty both by the stomach and the intestines, e.g., the leguminous vegetables. In these, the outer husk, the celluose, covers the nutritious elements, the starch and the albumins, contained in the cells, and prevents their digestion. It may therefore happen that a considerable portion of the albumin as well as of the starchy contents of such vegetables is lost. In other vegetables again, quite a large part of the proteid and starchy contents, as well as of the nutritive salts, may be lost owing to imperfect digestion of the cellulose, and also because, as we have already mentioned, they give rise, by virtue of their cellulose content, to increased activity of the intestinal movements. It would seem to me that the disciples of vegetarianism, in judging of the nutritive value of their diet, do not give sufficient consideration to the assimilative capacity of the intestine.
With a vegetable diet, much, if not all, depends upon the capacity for digesting cellulose. Animals are much better off in this respect than we are, since they have a specially adapted ferment, zylase, in their very large cecum. This ferment is absent in man, and is replaced by the intestinal bacteria, the various fermentative fungi we take in with the air ingested while eating and drinking, and in the food itself. These organ-isms act upon the cellulose in such wise that about 30 per cent. of it becomes soluble. Cellulose in general does not furnish any considerable amount of nourishment to us; yet, a portion of it may be assimilated. Through the action of the bacteria, not only are the useful nutritious substances inclosed in the cellulose set free, but also small amounts of fatty acids are formed by cleavage of the cellulose, such as acetic acid, butyric acid, etc., which also represent a certain nutritive value. Together with these, gases are formed. While an excessive quantity of gas is of no advantage, yet it exercises a stimulating effect upon the intestinal movements and favors the evacuation of the contents.
The bacteria of the intestine, however, also exert their decomposing action upon the albumin, and, in fact, upon any constituents of the food which have escaped digestion by the gastric and intestinal juices. When a person has ingested a large quantity of meat, it may happen that a portion of it will reach the large intestine still undigested, and here the bacterial action will very decidedly come into play. The body, however, cannot derive any nutritive benefit from the action of the decomposing bacteria upon the albumin in the large intestine, for, even though the resulting products may be absorbed, they are not assimilated in the same manner as other albuminoid nutrients, but, on the contrary, may exert an injurious and even poisonous action. Indeed, the general symptoms occurring after long-continued constipation, such as headache, nausea, mental depression, loss of appetite, etc., may be referred to the absorption of such poisonous products. The decomposition of albumins is greatest when the food remains a long time in the intestine, as is the case in constipation. It may be diminished by laxative mineral waters, since these shorten the time during which the food substances remain. The lactic acid bacilli act in the same way; they ferment the sugar contained in the foods and carbohydrates, form lactic acid, and disinfect and destroy the bacteria of decomposition. Any food rich in milk or sour-milk products, such as jogurt, kefir, etc., will restrict the processes of decomposition in the large intestine. According to Winternitz, decomposition may be entirely or almost entirely prevented by a milk diet.
During their progress through the intestine, all the fluids and other portions of the food which are capable of being absorbed are taken up, and, the farther the mass progresses down-ward, the more its liquid constituents are given off, until only the dry feces remain. The longer the feces remain in the intestine, the harder they become. When the diet consists principally of meat, the feces tend to be dry, but with more carbohydrates, especially in the form of sweets, they are more liquid. The carbohydrates cause fermentative changes which exert a stimulating effect upon the intestine, and cause the evacuation of the feces before they have had time to lose their fluidity. The result of this is, however, that the food substances are incompletely absorbed. While such starchy masses may induce diarrhea because of the fermentative processes, the dry condition of the stools produced by a meat diet may, on the other hand, cause constipation.
When there is too great a quantity of starch, a portion is usually found undigested in the stools. A diet containing a moderate quantity of starchy flour is best assimilated in the intestine, especially in the form of sugar, so that no trace of it is found in the feces.
The feces, in addition to the residue of the food, consist largely of the secretions of the intestines and of bacteria. Portions of the food may also be found, such as pieces of meat which have not been sufficiently masticated, elastic fibers, gristle, tissues, cells, and likewise the undigested husks of the cereals, which still contain albumin or starch granules, which, owing to insufficient cooking or faulty digestion, have remained intact. Certain food substances sometimes pass through the intestinal canal completely undigested. Only recently I found in the stools of a little girl of 6 years peas which had been eaten five days before, and had remained in their original form, entirely undigested, after an attack of colic and diarrhea. They had been swallowed unmasticated. Children should therefore never be given such indigestible foods unless the latter have been previously mashed up, as they have not yet acquired the habit of proper mastication. Children, and often hysterical or mentally affected adults, often swallow much more indigestible substances, and occasionally pointed objects, such as needles, without causing any injury to the intestines. Madinaveitia lately found in the stools of a woman a needle which had been swallowed some little time before, and had not given rise to any trouble. That such things are possible has, moreover, been shown by the experiments of Exner. He caused dogs to swallow needles and other pointed objects, all of which were afterward found in the stools. Exner showed that the presence of such objects caused a change in the shape of the intestine, which expanded to form a cavity in front of them, thus, one might almost say, running away from them. It would seem, consequently, that the throat and upper portion of the alimentary canal are more often injured than the intestines themselves after the swallowing of such foreign bodies.
As soon as the feces in their progress toward the external orifice have reached the colon, they exert pressure and irritation thereon, causing contraction of the gut and expulsion. This is a usual occurrence in persons who are normal, but there are many, especially young girls, who do not at once respond to this call of nature, thus causing the feces to remain a long time in the colon. The continuation of such a practice may induce such an habituation on the part of the bowel to its con-tents that their stimulating influence is lost. Obstinate constipation then results. This is most frequently found in women, as a consequence of this pernicious habit, and they are then obliged to resort to daily injections. I very frequently meet with such cases in my practice, especially among my French and American patients. Without their “enemas” these ladies never have a passage, unless they have been cured by a special treatment. It is therefore advisable that the call to void the stools be instantly followed whenever possible. When the intestine has lost the habit of responding to slight stimuli it becomes necessary to resort to very strong ones, in order to whip it up, as it were ; this is generally accomplished by resorting to injurious evacuants, which must then be constantly used.
Before closing this very important chapter, I would call attention to the decided influence of the condition of the mind upon the digestion.
In the process of digestion the mental state is of great importance. As with all the functions of the body, it is necessary to enter into it heartily, i.e., help it along; otherwise, it will be interfered with. This is especially well shown by Pawlow’s experiments on dogs. A lively, hungry dog, which gives its entire attention to its meal, entering into it body and soul, secretes large quantities of gastric juice, while a dog the attention of which is diverted, and which plays about while eating, will produce but little of it. The same thing occurs in man; children should, therefore, be strictly forbidden to play while eatingin fact, they should not be at all disturbed during this time. For, as has been shown by Pawlow’s experiments on animals, it is not only upon the gastric digestion that such disturbances act unfavorably, but also upon the digestion which takes place in the intestines, and the propulsion of the food therein. In man one may observe the same effect, and the satisfying of such an imperative demand as that of hunger should be accorded the full attention, if injurious results are to be avoided.