The movements of the bowels are dependent upon peristalsis in the absence of obstruction and upon the presence of a suitable solid, gaseous and liquid mass within. Constipation is usually-due to sluggish peristalsis while the term obstipation is limited to obstruction of greater or less degree. Diarrhoea is usually due to heightened peristalsis secondary to irritative or actually inflammatory conditions of the intestine itself. Increase of liquid, whether by increased ingestion, disproportion between secretion and absorption or exudation, especially the last, is an important factor. Brief or intermittent diarrhoea is also often due to gaseous tension. While a large quantity of solids in the bowel conduces to effective peristalsis, a small quantity of especially irritative solids may cause diarrhoea while astringent solids or those that are neutral in chemic action but which tend to form large masses, may cause obstruction. Thus, berry seeds may act sometimes as laxatives, sometimes in the opposite way, in the same or in different individuals.

A general rule, often ignored, but highly important, is not to combat either diarrhoea or constipation by setting up the opposite condition nor even by the use of agents which, without passing to the opposite extreme, still tend to produce the opposite pathologic condition.

The liberal use of water tends to produce freer movements of the bowels, not so much by directly increasing the water in the contents as by affording freer secretion, by lessening the need of marked absorption of water and by promoting vital processes generally. Large quantities of distilled water are apt to be irritating. Watery fruits, vegetables, soups and beverages, obviously act similarly to water as such but are more or less open to objection, by introducing fermentative material, toxic waste, xanthin derivatives, tannin etc., according to their individual nature. Water strongly impregnated with minerals may be irritating or astringent. Water taken very hot in small divided portions, especially if salted or containing fruit juice, sugar etc., to facilitate osmosis, is rapidly absorbed and is cholagogue and diuretic, rather than laxative. The most effective method of use of water as a laxative, is to take a glassful, cold, some time before breakfast.

Almost any substance soluble in water, acts as a cathartic if given in greater concentration than that of the blood serum, by drawing water into the bowel and, probably, in most instances, by reflex irritation also. The use of salines and glycerin for this purpose is rather medicinal than dietetic. Sugar, in various forms, is laxative, but it should not be used in so great an amount as to cause glycosuria, obvious gastro-enteric irritation, nor fermentation. 100 grams at once or 200 in one day, should be considered the limit.

Saccharine fruits combine the effects of water, salts and sugar and also contain moderate quantities of cellulose. There is considerable variability in their laxative effects. Given a not too marked coprostasis with fermentation and some exudation behind it, the increase of fermentation and peristalsis produced by fruit, is very apt to cause an explosive diarrhoea. Indeed, even the progress of a meal through the stomach and upper intestine, may compress the gass ahead so as to result in catharsis, somewhat after the principle of the quill potato-shooter, although, even in the most extreme cases, there is never an uninterrupted column of air in the bowel, under high pressure. Considerable idiosyncratic factors exist with regard to the laxative effects of fruit. A single sour apple for some persons, sweet apple for others, dish of stewed prunes for still others, may act very promptly and efficiently, while others will have no appreciable effect from what appears to be excessive indulgence.

The paradox that solids pass through the bowel more quickly than liquids, is explained by the presence of the valvulae conniventes. Any solid not so large as to block the alimentary canal, at least at the sphincters, and which is smooth and large enough to ride upon the crests of the valvular waves, will usually be evacuated in the first passage occurring after a period of four or five hours after ingestion, while the softer parts will be evacuated, mostly in the passage of the next day and somewhat in the passage of the second day afterward.

Large smooth seeds, berries, corn, peas, beans, and lumps of beet, radish etc., imperfectly masticated and not sufficiently softened by cooking for thorough disintegration during starch digestion, will, if no excess of fermentation or mechanic irritation occurs, pass through the bowel more rapidly than the properly prepared food mass with which they were introduced, except that they may be retained in the lower bowel. Thus, residue of this sort, under the conditions named, does not act as a laxative. If the conditions are not fulfilled, such residue may, on the one hand, produce an irritative diarrhoea, on the other a coprostasis. Such masses, due to the neglect of proper comminution of food, may, of course, often substitute a mild diarrhoea for a state of constipation, but should not be used with this end in view.

Caraway seeds, seeds of raspberrfes and blackberries, scales of apple and pear cores, oat husks etc., are very often found in the stool sieve - a very instructive, simple, cleanly, and much neglected instrument - a week or two after ingestion and, in elderly persons of sedentary habit, not infrequently several weeks after the time of their ingestion. Sometimes there is obvious fermentation and mucous catarrh in the pockets of the colon in which these substances lodge, sometimes they form an obstruction quite analogous to a dam of pebbles in a stream, sometimes diarrhoea results from the irritation at the sites of retention or, if this site is the caecum or appendix, very serious inflammatory lesion may result, with septic consequences. As a rule, if the intestinal mass is otherwise sufficiently bulky and soft, such small particles are imbedded in it and swept through without doing harm. Yet, obviously, their action is too uncertain to be depended on therapeutically.