Disturbances of digestion may exist in pro longed and serious forms when there is no disorder of the stomach, due to mischief of some kind or other in the small or large bowel err other abdominal organs. This is easily under stood when one recalls the important part of digestion carried on in the small bowel in par ticular, by the chemical action of digestive juices secreted by the glands in the bowel wall, and poured into the bowel from the liver and sweet-bread, all of which facts have been care fully stated in the preceding section.
The integrity of the digestive process in the bowel is dependent upon a much larger number of circumstances than that of stomach digestion, and the possibilities of disturbance correspond ingly increased. For, in the case of the stomach, if the entrance to it and ezit from it are un impeded, if the tone of its muscular wall is unimpaired, and if the juice produced within its own glands is sufficiently active, all the conditions exist for healthy stomach digestion. But in the case of the bowel, intestinal diges tion depends not only on the integrity of the bowel itself but also upon the harmonious co operation of other organs outside of it, notably the liver and sweet-bread. As regards the bowel itself, we have seen that it is of considerable length, about 26 feet, including the large bowel. In a great part of this length the tube is compara tively narrow, and at the place where it enters the large bowel, the ileo-czecal valve (p. 199), the width is greatly reduced. Any growth or thickening at any part of the wall along its whole length might easily gravely constrict its fairway, while the pressure upon the wall by any inflam matory mass or new growth outside of it might easily block it completely. Then the tube of the small bowel is coiled irregularly within the centre of the abdominal cavity, the smooth external surface of the intestine permitting the coils to glide easily upon one another. But any inflammatory mischief within the cavity interferes with the smoothness of this surface and readily causes one coil to adhere to another, limiting its freedom of movement. Inflamma tion may in this way not only glue together, se to speak, a mass of coils which ought to be able to roll and glide over one another, but thin gluing process might bind down a coil in an inconvenient position, producing sharp bendn or" kinks" on the tube, which would seriously hinder .he pas age of the food-stuffs along the canal of the tube.
But we have seen that the contents of the intestine are propelled along the tube by a wave - like movement (peristaltic movement) that passes along the intestinal wall in a spiral manner. As this wave slowly passes along, it constricts the tube at the part over which it is passing, and anything within this part of the tube, at the time the peristaltic wave is passing over it, is squeezed on, so to speak, into the next part of the canal. So the contents are gradually propelled from one end to the other.
Any inflammatory adhesions between sepa rate coils of the bowel, or between coils of the bowel and other structures outside of them, would upset the progress and hinder the effect of this peristaltic wave movement.
But the bowel being loosely coiled in the centre of the abdominal cavity, and attached to the back wall of the cavity by a delicate membrane, the mesentery, it is always possible for a coil or a mass of coils, by an exaggeration of the normal peristaltic movement, to roll right round on itself and thus cause a complete twist in the tube. Such an occurrence is called volvulus.
Again, the mucous or inner lining membrane of the intestinal tube is subject to catarrhal affections, just as the mucous lining of the nose or throat or stomach is. Such catarrhal swell ing alters the proper secretion of the tubular glands, embedded in the mucous lining, either diminishing it seriously or increasing it and altering its character, just as the ordinary healthy secretion of the nose is affected by a cold, being in one variety diminished and so causing excessive irritability and dryness of the nostrils, and in another variety being excessive, watery, and mucous. Thus, speaking broadly, digestion within the bowel may be disturbed either by (1) some irregularity of the secretion from the wall of the bowel itself, or (2) by some interference with the freedom of the bowel in the movement of its wall.
Thus there is a class of disorders of the bowel which spring from some alteration in its secre tion, and a class of disorders which spring from some change in its mobility. But as we have said, it is not a single juice, produced within the wall of the bowel itself, that carries on the digestion in the bowel ; on the contrary, digestion within the canal of the bowel is much more dependent upon juices imported from organs outside of it, and so the chances of disorder are greatly multi plied. Thus any one of the numerous diseases of the liver may manifest itself by a disturb ance of intestinal digestion, provided it affects the amount and quality of the bile delivered to the bowel, and so also may any one of the at present ill-defined affections of the pancreas do the same by affecting the amount and character of the pancreatic juice.
It has also been pointed out that the veins which carry off the blood which has circu lated through the stomach, bowel, spleen, and pancreas unite to form one large vein, the portal vein (p. 200), which passes to the liver. Any obstruction to the flow of the portal blood •through the liver would lead to engorgement, or congestion of all the veins of the organs named, which would be a very serious result.
Of indigestion arising in the bowel, therefore, may one say most emphatically what has been said of indigestion arising within the stomach, that it is no mean task to unravel its mazes and to arrive at a correct judgment of its true character and cause. One may, therefore, ask the same question regarding the bowel we have already tried to answer regarding the stomach, how does one arrive at a decision re garding the nature and cause of its disturbance?