Part 105

The more tardy the digestion in the stomach the more highly charged with acid is the gastric juice. According to Wright, the degree of alkalinity of the saliva is in proportion to the acidity of the stomach fluids, and Bence Jones has observed that during the excretion of acid in the stomach the total alkalinity of all alkaline digestive fluids is increased. The lesson is thus learned that a too careful preparation of food, so as to shorten and lessen gastric labor, diminishes the activity of the gastric juice as well as that of all other digestive fluids.

Intestinal digestion begins when the softened mass passes through the pylorus. This mass (chyme) is composed of (1) the products of gastric digestion which have not been absorbed--peptone, dextrose, levulose, peptonized gelatin, with mucus and gastric juice; (2) all matters which have escaped digestion--the starch of vegetable substances, dissolved gelatin and albumen which have not been peptonized, and some unaltered muscle-structure; and (3) fat, fatty acids, and cellulose upon which neither saliva nor gastric juice has had any influence (Ewald).

This complex semi-fluid mass with an acid reaction enters the duodenum and comes in contact with fluids and ferments destined to work remarkable changes in its composition. The first of these fluids is the bile, which is alkaline and composed of the glycocholate and taurocholate of sodium, cholesterin, soaps, etc., phosphates and carbonates of lime and sodium, chlorides of potassium and sodium, bile-pigment, etc. The outflow of bile is excited by the contact of the chyme with the orifice of the bile-duct. When the alkaline bile is mingled with the acid mass in the duodenum, it neutralizes its acidity, precipitates the peptones, and therefore stops all further action of the gastric juice. Fats containing free fatty acids are emulsified, soaps being formed by a combination of the alkalies of the bile with the fatty acids. Lastly, bile hinders fermentation in the intestine and acts as a purgative by exciting peristalsis. Absorption is probably also favored by bile, as it has been found that emulsified fats pass more readily through an animal membrane which has been wet with bile.

{622} As far as we now know, the function of the bile is to neutralize the acidity of the duodenal contents, and thus pave the way for the action of a digesting fluid of much greater potency and of much higher function.

This fluid, the pancreatic juice, is composed of inorganic salts, albuminoids, and certain specific ferments, and has an alkaline reaction. It has a threefold operation upon the softened mass with which it now comes in contact: 1. The starch of vegetable matter, which has been only slightly acted on up to this time, is now rapidly converted into grape-sugar by a peculiar diastatic ferment more active than any other known ferment. 2. Albuminous matters (proteids) which have escaped digestion in the stomach are changed into a soluble and absorbable pancreas--peptone. Trypsin is the active ferment in this case (Kühne), and it is only in alkaline or neutral solutions that the albuminoids are readily dissolved. The necessity of neutralization by the alkaline bile is thus demonstrated. 3. A ferment distinct from the others splits the fats into fatty acids and glycerin, and emulsifies them so that they can be taken up by the lacteals lower down.

Experiments made by mixing albuminates with pancreatic gland-extract, under favorable conditions, show after a certain time the presence of leucin, tyrosin, hypoxanthin, and asparaginic acid. In a feebly alkaline or neutral solution a faint putrefactive odor is soon noticed, with the development of bacteria; ammonia, sulphuretted hydrogen, hydrogen, and carbonic acid--evidences of the putrefaction of albumen--are also detected.

It is difficult to tell when normal digestion in the intestines ends and putrefaction begins. The conclusion is, that the normal action of pancreatic juice (trypsin) gives origin to bodies met with in the ordinary putrefaction of albumen. This thin border-line between normal intestinal digestion and the decomposition of the intestinal contents has an important bearing on the facts of intestinal indigestion.

The intestinal juice performs a minor but independent part in digestion. It converts albuminous matter into peptone, and hydrated starch into sugar. Its function is therefore supplementary to that of the gastric and pancreatic secretions.

When food enters the mouth the process of digestion begins, and all the activities of the glands concerned in digestion are probably at once set in motion. Mastication excites, by reflex action, pancreatic secretion; the acid chyme touches the orifice of the common bile-duct and stimulates the outflow of bile; the neutralized chyme next invites pancreatic digestion. For the integrity of intestinal digestion it is required that mastication and stomach digestion should be normally performed.

The intestinal movements which are so necessary to digestion by making successive changes in the position of the intestinal contents are {623} controlled by nervous arrangements, but may occur independently of the central nervous system. The ganglia of Auerbach and of Meissner in the intestinal wall are sufficient for the development of peristaltic waves. The irritation of the mucous membrane by food, hyperæmia, and the pouring out of digestive juices, and intestinal movements, are parts of one process. Paralysis by section of the splanchnic leads to hyperæmia of the intestinal vessels and increased peristalsis; stimulation of the splanchnic causes anæmia of the intestinal wall and arrest of movement. Local cold by producing anæmia brings about the same result.

The products of digestion as they pass toward the jejunum consist of diffusible peptones, sugar, emulsified fats and oils, and substances which have escaped digestion, as fragments of muscular fibre, starch-corpuscles, connective tissue, hairs, or other foreign matters. The bowel contains also carbonic acid, hydrogen, nitrogen, sulphuretted hydrogen, and marsh gas. The mass, alkaline or neutral in the duodenum and jejunum, becomes acid in the ileum from the putrefaction of albumen and fermentation. The peptones and sugar pass by osmosis into the blood-vessels of the portal system and thence to the liver. In the liver the sugar is converted into glycogen (carbohydrate), and stored in the liver-cells until needed for the maintenance of animal heat and for the nutrition of the tissues. The peptones are used in part to supply the nitrogenous waste of tissue, but much of the albuminoid matter is broken up in the liver into glycogen and urea, the latter of which is excreted by the kidneys as waste matter.

The minute granules of oil in emulsion are taken up by the epithelial cells covering the villi; thence they enter the adenoid tissue of the villi on their way to the lymphatic radicles, the lacteals. From here the passage is open to the underlying lymphatic vessels and to the larger abdominal lymph-vessels and the thoracic duct beyond.

Intestinal digestion is not completed and the body does not receive its pabulum until the products of digestion have reached the liver and the thoracic duct.

ETIOLOGY.--It is usually said that intestinal dyspepsia is more common in women than in men, but the contrary is the rule. Some of its most common causes--over-eating and the eating of indigestible food--are especially vices of men.

It is more frequent between the ages of forty and fifty, but no age is exempt. Infants at the breast, children of any age, adults, and old men and women are alike subject to it. Men in middle life begin to suffer from the imprudence and carelessness of youth and from the anxiety and cares of business. The indulged children of rich parents and improperly bottle-fed infants frequently suffer.

Heredity and idiosyncrasy have a certain influence in determining the prevalence of intestinal dyspepsia. The distaste for and inability to digest vegetables, fruits, and fats are often peculiarities of family history. The occurrence of cases in the same family is often explained by improper food, bad cooking, and irregular hours, to the evil influences of which all the members are similarly subjected.

All conditions of the organism which result in a depraved or altered blood-supply, as anæmia, primary and secondary rachitis, chronic syphilis, and continued febrile diseases, are causes of intestinal indigestion. {624} The connection of the indigestion of fats with the strumous diathesis and with phthisis is undisputed. J. Hughes Bennett traced the origin of phthisis to defective fat-digestion; strumous indigestion and the indigestion of fat are synonymous terms.

Debilitating influences, such as bad air, want of cleanliness and outdoor exercise, impair functional activity in the intestines as elsewhere. Sexual excesses, but especially masturbation, have a special influence for evil in this direction.

The influence of the mind upon the digestion of starch and fats is even greater than upon gastric digestion, for no other reason perhaps than that the former is a more complex function and less easily relieved than the latter. Prolonged or excessive mental labor does not do so much harm as mental worry, over-anxiety, and the strain and overwork of business. Professional men--lawyers, physicians, and clergymen--who become over-burdened with responsibilities, and who sympathize too much with the distresses of others, are very prone to suffer. The careworn face with lines about the mouth and forehead is one of the plainest signs of duodenal defect. The proper secretion of the juices of the intestine and normal peristalsis are impossible where brain and nerves get no rest. The too rapid mental development of the children of the present day is a fruitful source of weakened fat-and-starch digestion and of impaired development. So long as children are sent to the public school at four and six years of age, there will continue to grow up a precocious race with active brains in feeble bodies. This injurious result is largely brought about by the direct interference of premature brain-development with the complex intestinal processes of digestion and absorption.

Wealth, with ease and inactivity, and sedentary occupations, contribute to the same end by lessening the need of food, and thus debilitating the organs of digestion by inaction. Sedentary pursuits, especially those in which the body is bent forward and constricted or compressed at the waist, interfere with active function in the intestine. This is the case in tailors, shoemakers, etc. Tight-lacing in women and a too tight trouser-band in men are injurious.

Hot climates, especially when combined with dampness, lead to disorder in the intestine and liver. This effect is most marked among persons coming from colder climates, as among the English in India, who keep up the habits of eating to which they have been accustomed at home. The lessened demand destroys the appetite, and stimulants and condiments are resorted to to whip up the inactive functions. The intestine is loaded with a mass of crude, unaltered matter which can with difficulty be disposed of. Chronic indigestion results, varied with acute attacks of diarrhoea or dysentery. The portal system is filled with an excess of albuminoid material which the liver is unable to store away. The excess is got rid of by conversion into uric acid. Lithæmia and chronic congestion and enlargement of the overloaded liver result, with their many attendant evils.

Over-eating occasions first gastric and then intestinal indigestion by the {625} entrance of unaltered food into the duodenum. Eating without hunger often involves the taking of food which the body does not need and which the stomach cannot digest. Diners-out rarely go through a season without one or more internal revolts. A too-varied diet, a dinner of many dishes, is faulty in variety as well as in excess. On the other hand, a too great sameness in diet and the prolonged use of one or two articles of food which are not easy of digestion, and which have a great deal of waste, fatigue and then disorder intestinal digestion. This is a fault into which children are often allowed to fall.

Indigestible food and an excess of starchy or fatty food conduce to disorder of duodenal digestion. In conditions of debility and anæmia and in the convalescence of fevers the deficiency of saliva involves an inability to digest starch in the mouth and points to a corresponding want in the duodenal secretions. The improper use of alcoholic liquors, taking them on an empty stomach between meals and in excess, tends to direct irritation of the mucous tract. Condiments in large quantity have the same effect.

Irregularity in the hours of eating and a faulty distribution of the amount of food disturb the perfect working of the mechanism of digestion. Very light breakfasts and very late and large dinners are injurious. The habit, now quite general in cities, of deferring the breakfast proper until midday, leaves the system too long--fifteen to sixteen hours--without proper food and weakens digestive activity. Intestinal indigestion is very common among Americans who have lived abroad and adopted European customs.

Another cause which is unfortunately very common is the imperfect mastication and insalivation of food, due to too great haste in eating, to defects in the teeth or gums, or to a deficiency of saliva. The saliva no doubt sometimes possesses a feeble diastatic power, although abundant in amount. Carnivorous animals bolt their food, but vegetable-eaters must masticate. Slow mastication transforms starch into sugar, and at the same time excites secretive activity in the glands of the digestive tract, especially in the pancreas. The more thoroughly this preliminary function is performed the better preparation is there for the subsequent acts of digestion.

The chewing of tobacco, a wretched habit which is much less common now than formerly, and to a less extent the habit of smoking, are causes of deficient, altered, or depraved saliva, and secondarily of altered pancreatic secretion. The thin smoker grows fat when he abandons the weed.

The normal functions of the intestines are interfered with and indigestion is set up by constipation. Every one has felt the activity in digestion which accompanies the regular habit of defecation, and the torpor and oppression which depend upon an unemptied colon. "There is a concert of action in virtue of which the whole muscular apparatus of the digestive tube sympathizes with that of the large intestine. This concert of action, which induces pathological states, is the reason why in the {626} physiological state a regular contraction of the whole intestinal tube, including the stomach, is the consequence of the regular contraction of the large intestine."

An excess of acid in the stomach would enfeeble the solvent power of the intestinal fluids by antagonizing neutralization by the alkaline bile; the same effect follows any cause which prevents the outflow of the bile, as the plugging of the common bile-duct by mucus and epithelium in catarrh or by an impacted gall-stone. The emulsification of fats is incomplete and decomposition in the intestine follows. The antagonism of the saliva and the gastric juice, of the gastric juice (or the chyme) and the bile, must preserve their delicate and nice adjustment in order for digestion to be properly performed.