INTESTINAL INDIGESTION.
BY W. W. JOHNSTON, M.D.
NATURE.—The term indigestion in its most common meaning refers to gastric indigestion only. This limitation has arisen from the fact that gastric digestion has been more thoroughly understood than intestinal digestion, and because the symptoms, flatulence, acidity, eructations of gas, pyrosis, and vomiting of unaltered food, are readily referred to the stomach as their source. Intestinal digestion has not been well known until within a recent date, and its phenomena in disease have been mistaken for other pathological conditions.
From the important and complex function of the intestinal juices, and the very great share they take in the solution of food, there must be many phases of departure from the normal state. The processes of intestinal digestion are more intricate than those of gastric digestion, of a higher grade, and the chemical reactions are more numerous, depending upon the participation of the bile, the pancreatic juice, and the succus entericus; while intestinal absorption is a more complex act than that of gastric absorption.
A brief review of the physiology of intestinal digestion will be of aid in making clear its pathology.
The object of all digestion is to make such a solution of the ingesta that they may pass through animal membrane and so enter the system. Mechanical disintegration and simple solution do something toward this, but for substances insoluble in water a more thorough change is brought about by ferments which convert insoluble into soluble compounds.
The process of digestion begins in the mouth. Mastication breaks up the masses of food; the saliva softens them, dissolves soluble substances, as salt and sugar, and thus the pleasures of the palate are enhanced. The ferment ptyalin acts upon starch (boiled starch being more rapidly altered than unboiled), and changes it to dextrin and grape-sugar, both of which are diffusible through animal membrane, entering lymph-spaces and blood-vessels. The greater part of the saliva secreted is swallowed with the food or in the intervals of eating. The amount formed in twenty-four hours varies from 1500 gm. (Bidder and Schmidt) to 700 gm. (Tuczek). It must therefore serve some ulterior purpose in the stomach. Ewald1 says that saliva converts starch into sugar in acid as well as in alkaline and neutral solutions. But Langley2 asserts that the ferment of saliva is destroyed by the hydrochloric acid of the gastric juice. The longer food is subjected to mastication and insalivation, the more thorough is the mouth digestion and the better prepared is the mass for the action of the gastric and intestinal juices. It is asserted that fatty matters are emulsified to a certain extent by the alkaline ferments of the saliva.