The composition of the colon contents, the feces, is very complicated and highly variable, depending very largely upon the character of the food. The bowel discharges of the nursing infant consist of fragments of undigested curds, fat, bile and a small amount of mucus. The odor of a healthy infant's stool is slightly acid, and yellowish in color. The stool of an adult who subsists upon an ordinary mixed diet contains a considerable amount of food residues, seeds and skins of fruit, cellulose from vegetables, and such whole-grain cereals as oat-meal and cracked wheat, and also contains one or two per cent of starch, about the same amount of fat, and three or four per cent of protein. Sugar is not present. The color is usually dark brown, often black, and the odor putrid. The form varies to a marked degree.
The stools of a person who subsists on a natural non-flesh diet closely resemble those of a healthy infant. The odor is not putrid, but may be slightly sour.
Strassburger has shown that about half the solids of fecal matter is made up of bacteria. When the stools are putrid it is because of the dominance of the special bacteria which give rise to putrefaction. In sour smelling stools, however, the bacteria present are chiefly those of the sort which cause fermentation and give rise to acid. The sour odor is due to the presence of acetic acid, which is more or less volatile at low temperatures. Lactic acid is also present. As it is non-volatile, its presence is shown only by chemical tests, not by the odor.
The general belief that the feces or stools consist chiefly of the unusable remains of foodstuffs is entirely erroneous. As a matter of fact, even under the most unfavorable conditions, the feces contain really very little food material.
The chief constituents of the feces are as follows: Bile, remains of digestive juices, especially of the pancreatic juice, mucus, excretory substances thrown off by the intestinal mucous membrane, microbes and various poisons produced by microbes, such as indol, skatol, pyrrol, and numerous other poisons, together with some small amounts of the various food principles, and water.
The composition of the stool varies greatly according as the diet contains much or little of vegetables. On a vegetable diet the feces contain much cellulose, and with the cellulose are increased quantities of undigested protein and starch. The amount of fat does not vary much, and sugar is never present.
The weight of feces varies very much with the diet, increasing with a vegetable diet, and diminishing with a diet composed chiefly of animal substances. Food which contains much cellulose passes through the intestine much more quickly than does animal food, and hence contains more water and undigested food principles. The total weight of the feces for twenty-four hours with a mixed diet is about five ounces, of which three-fourths is water. With a vegetable diet the weight is double, the proportion of solid matter being slightly greater.
The reaction of the feces is neutral or slightly acid on a vegetable diet, and strongly alkaline on a flesh or mixed diet. This difference in reaction is due to the difference in the flora or species of bacteria which are present. Feces that are rich in protein, the result of a mixed or flesh diet, contain enormous quantities of putrefactive bacteria, which produce alkaline substances in decomposing the proteins - ammonia, ptomaines, and various toxins. When considerable quantities of starch are present, as with a vegetable diet, with very little protein, acid-forming bacteria are dominant, and hence the feces have an acid or neutral reaction.
This difference in reaction is one of the most important of all the various characteristics of the feces, since it suggests at once the general character of the flora, and thus points to the toxic or nontoxic character of the stool.
Roger calls attention to more than one hundred and sixty different species of bacteria which have been found in the feces. Of these, more than one-third were found to possess pathogenic or disease-producing properties. Distaso points out more than twenty species of putrefactive bacteria which are found in the stools of flesh eaters, all of which produce very highly toxic products. One of the most common and abundant of these is the Bacillus of Welch, which produces enormous quantities of offensive gas and highly active poisons. This microbe, as well as the other putrefactive organisms which are found in the feces, is found in an active growing condition in butcher's meat and fresh flesh foods of all sorts, as well as salted and dried fish. This is doubtless the chief source of the dangerous bacteria which carry on in the body the same putrefactive processes to which they give rise outside of the body.
The number of these microbes in the feces is something prodigious. They often constitute from one-third to one-half the total weight of dried feces. Strassburger estimates the weight of the microbes produced in the intestines in a single day at not less than one-quarter of an ounce, and the number more than one hundred trillions, of which a large proportion may be poison-forming organisms. Only a small share of the bacteria are found alive in the feces (one per cent, according to Strassburger), but all have been alive and have each produced its portion of poisonous substances in breaking up the protein upon which it feeds.
The study of these bacteria is one of the most important fields of research at present before the bacteriologist, for it has been clearly shown that the condition of the flora of the intestine is one of the most important of all factors in determining health or disease, long or short life. Of this subject we shall learn more in a subsequent chapter.