Feces

Feces, also stool, excreta, or residual waste materials, evacuated from the bowels. Through peristalsis (involuntary intestinal contractions) and digestion, partly digested food begins to assume the aspects of feces when it passes from the small intestine to the large intestine. In a healthy digestive system, feces consist of undigested and indigestible food products such as mucous secretions and cellulose; traces of intestinal juices from the liver, the pancreas, and other digestive glands; undestroyed enzymes; leucocytes; epithelial cells; cellular debris from the intestinal walls; fat globules; nitrogenous protein products; mineral salts; water; and large numbers of bacteria. Probably one-third of the weight of human stool is composed of bacterial debris; an average of 100 billion bacteria are excreted daily by each human being. More than 75 different kinds of bacteria are found in stool. The unpleasant odor of human feces is chiefly due to the presence of the two-ringed organic compound skatole, C₉H₉N. In monotreme mammals, in birds, reptiles, and fishes, and in many lower animals, urine is mixed with the feces before evacuation.

The physical character and chemical nature of feces are not entirely influenced by the nature of the diet. For example, the feces produced from a diet consisting exclusively of carbohydrates are similar in composition to those produced from a diet consisting exclusively of proteins. In starvation, the feces are reduced in quantity and almost black in color, but their chemical constitution is essentially unaltered. A bulky stool is produced by foods rich in cellulose. The diet of the human fetus is entirely liquid, but shortly after the child is born it evacuates a semisolid, dark greenish-brown fecal mass known as meconium.

Medically, the examination of feces is an important diagnostic procedure. Both gross and microscopic analyses are used to determine whether the digestive organs are functioning properly. For example, a light-colored or fatty stool may indicate a pancreas disturbance, and a black stool may indicate excessive bile functioning. Constipation may produce a hard stool, and those of persons with indigestion may be soft and watery. The most important use of microscopic analysis of feces is to determine the kinds of parasites present, especially as related to disease. In diseases of the pancreas, proteins are not well digested, and an excess of muscle fibers may be present in the stool (azatorrhea). An ulcer or cancer in the stomach or large intestine causes small amounts of blood to be present in the feces. Larger amounts of blood produce a black stool. Bleeding from the lower portion of the intestine or from the anus (as a result of hemorrhoids) produces unaltered blood in the stool, coloring it bright red.

Guano, the dried excrement usually of seabirds, and manure, the feces of such domestic animals as cattle and horses, are widely used as fertilizers. See Fertilizer.