Over-eating occasions first gastric and then intestinal indigestion by the 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.8
8 "The familiar act of chewing is seldom a subject of reflection, yet it throws into motion a more complicated system of levers, accompanied by a drain of fluids from more curiously adapted apparatus, than the arts can parallel" (Leared, On Indigestion, London, 1863, p. 3).
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 physiological state a regular contraction of the whole intestinal tube, including the stomach, is the consequence of the regular contraction of the large intestine."9
9 Trousseau, "Les Dyspepsies," L'Union médicale, tome xi., 1857, p. 313.
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.
Diseases of the pancreas seriously embarrass digestion in the intestine. Lesions of this organ, as catarrh of the duct, cancer, fatty degeneration, etc., may result in impaired emulsification of fats, fatty diarrhoea, and wasting.