To fully comprehend the influence of various habits and conditions in developing constipation, it is necessary to have in mind the mechanism of defecation and the conditions essential to the normal colon action. The several acts by which the colon is emptied of its contents may be briefly summarized as follows:

1. Contraction of the diaphragm - a deep breath.

2. Contraction of the abdominal muscles.

3. Pressure of the thighs against the abdomen as in the squatting position assumed by the savage.

4. Reflex contraction of the abdominal muscles.

5. Contraction of the colon.

6. Relaxation of the anus.

7. Contraction of the levator-ani muscles. Any influence which interferes with a single one of these seven steps in the normal process of defecation may give rise to constipation, and when the disturbing influence is of such character as to interfere with several factors, the result is certain to be an extremely obstinate form of colon inactivity.

The causes of constipation may become operative either before or during the action of defecation. In order that normal defecation should occur, it is necessary that fecal matters should reach the pelvic colon in condition to be expelled from the body, and that the pelvic colon should be free to rise out of the pelvis, so that it may discharge a part of its contents into the rectum; and it is then essential that there should be no interference with any of the several factors which enter into the normal act of defecation.

Among the causes that may operate to prevent the proper preparation of the bowel for the act of defecation through the accumulation of the bowel contents in the pelvic colon, are the following:

1. Deficient bulk of intestinal contents. If the amount of the intestinal contents is too small to distend the pelvic colon, the bowel will not be stimulated to action. This condition naturally results during fasting, and may also result from the use of a concentrated diet. A diet largely made up of animal foods; that is, fish, flesh, fowl, eggs and milk, is always a concentrated diet, since these materials are almost entirely digested and absorbed, leaving no residue. On the other hand, vegetable foods, with a few exceptions,- - such as the banana, potato, fine flour bread, and polished rice, - contain a considerable amount of cellulose, which in human beings is indigestible.

2. A spastic or contracted condition of the bowel in the transverse, descending, or iliac colon may hold back the intestinal contents, preventing them from reaching the pelvic colon, and so may interfere with normal bowel action. This condition exists in nearly all persons suffering from colitis, the most common seat of which is the descending colon. The effect may be almost the same as that due to organic change, as from ulcer or adhesions.

3. Adhesions, by interfering with the normal contraction movements of the colon, may seriously cripple its function. These adhesions may be the result of peritonitis due to chronic infection of the mucous membrane extending through the wall of the bowel to its peritoneal surface. Such adhesions may occur between any part of the colon and the abdominal wall, but are most likely to occur in the lower part of the colon. Adhesions of this part of the colon are in the writer's experience very likely to be found present in cases of extremely obstinate constipation.

4. Redundancy of the colon is another frequent cause of constipation. The overloaded colon is gradually stretched, until it may acquire nearly double its normal length. The redundant colon often becomes folded upon itself, and adhesions form, giving rise to kinks which produce mechanical obstacles to the forward movement of the intestinal contents.

5. Incompetency of the ileocecal valve, by preventing the forward movement of the intestinal contents, hinders the normal filling of the pelvic colon, and so leads to constipation.

6. Ordinarily, the whole bowel is not emptied in the act of defecation. The length of the colon is such that the residue from two or more meals may be present in different parts of the intestine at the same time. For example, the supper residue may be passing into the cecum while the dinner residue occupies the transverse colon and the breakfast residue is in the pelvic colon ready to be dismissed.

The descending colon is normally found in an empty state. When the intestinal contents are pushed from the transverse colon over into the descending colon, they are not long retained, as in other parts of the colon, but pass rapidly down to the pelvic colon, which seems to be, intended by nature for a sort of discharging reservoir, in which the fecal matter accumulates until a sufficient degree of distention of the bowel has been induced to stimulate peristaltic action.

A lack of this distending stimulus, which is essential to bowel activity, is a cause of constipation in a large number of persons whose pelvic colons have been over-distended. In such persons an extremely bulky diet is necessary to fill the pelvic colon to such a degree as to bring about the reflex movements which induce normal bowel action.

In persons who are chronically constipated the descending colon is often constantly filled. The long contact of the poisonous fecal matters with the mucous membrane gives rise to infection. This is colitis. Colitis causes contraction of the, bowel, thus becoming a hew and most potent cause of constipation. The contraction produced by colitis not only obstructs the bowel, but also sets up antiperistaltic movements, thus reversing the action of the bowel and carrying material back to the ascending colon and cecum. Normally, the anti-peristaltic contractions start at the middle of the transverse colon and do not involve the lower half,of the colon. But when colitis and spasm are present, the reverse movement extends even to the pelvic colon. This fact, discovered by Case, explains the peculiarly irregular and erratic bowel movements characteristic of colitis.

7. By compression of the waist, such as results from the wearing of corsets and tight dresses, the action of the diaphragm is greatly crippled. This may be one reason why women in general suffer from constipation more than do men. The feeble condition of the diaphragm and other breathing muscles, which is the natural result of neglect of exercise, produces a similar effect in both men and women.

8. A feeble and relaxed condition of the abdominal muscles, the result of a sedentary life, and especially of a stooped and relaxed posture of the body in sitting or standing, will necessarily interfere with both voluntary and reflex contraction of these important muscles, which is an essential factor in normal defecation. When the colon has been long over-distended by neglect, and relaxed by the long-continued use of the warm enema, its power to contract is necessarily greatly diminished. This condition of the bowel not only prevents inefficient normal defecation, but the efficiency of the bowel may be still further interfered with by adhesions and kinks.

9. Hemorrhoids, fissures, ulcers, fistulas, and simple irritation of the mucous membrane in the anal region, may cause spasm or abnormal tightness of the anal muscle, so that the ordinary reflex is insufficient to cause relaxation of the muscle, and it thus becomes a mechanical obstacle to bowel movement.

10. The levator-ani muscle frequently becomes so weakened by continuous over-stretching, as the result of accumulation of hard fecal matters in the rectum, that it loses its power to contract. This condition may also be induced by proctitis, a common result of constipation.

When the rectum walls are thus weakened and paralyzed, the rectum, instead of being always empty except during defecation, always contains more or less fecal matter, the constant, contact of which with the mucous membrane produces loss of sensibility and chronic catarrh or proctitis, and often gives rise to hemorrhoids, anal ulcer, abscesses, fistula and local affections.

It is thus apparent that in all cases of constipation there is a definite reason for intestinal inactivity. In every case of really serious constipation - that is, cases which are not relieved by regulation of diet-careful inquiry must be made for the purpose of ascertaining the exact conditions which are inter-fering with normal intestinal movement, including both the exciting and the predisposing causes of these conditions, which will be considered at length in succeeding pages.

In discussing the causes of constipation, we will consider first of all the influence of habits of life upon the function of defecation, and will then notice various morbid conditions in different parts of the alimentary canal, which may give rise to constipation.

Lower jaw of a Malkelkos Indian.

Lower jaw of a Malkelkos Indian.