Feces

Feces (or faeces) are the solid or semisolid remains of food that could not be digested in the small intestine. Bacteria in the large intestine further break down the material. Feces contain a relatively small amount of metabolic waste products such as bacterially altered bilirubin, and the dead epithelial cells from the lining of the gut. Feces are discharged through the anus or cloaca during defecation. Feces can be used as fertilizer or soil conditioner in agriculture. It can also be burned as fuel or dried and used for construction. Some medicinal uses have been found. In the case of human feces, fecal transplants or fecal bacteriotherapy are in use. Urine and feces together are called excreta. The distinctive odor of feces is due to bacterial action. Gut flora produces compounds such as indole, skatole, and thiols (sulfur-containing compounds), as well as the inorganic gas hydrogen sulfide. These are the same compounds responsible for the odor of flatulence. Consumption of spicy foods may result in the spices being undigested and adding to the odor. The perceived bad odor of feces has been hypothesized to be a deterrent for humans, as consuming or touching it may result in sickness or infection. Human perception of the odor may be contrasted by a non-human animal's perception of it; for example, an animal who eats feces may be attracted to its odor. Feces are discharged through the anus or cloaca during defecation. This process requires pressures that may reach 100 mm Hg in humans and 450 mm Hg in penguins. The forces required to expel the feces are generated through muscular contractions and a build-up of gases inside the gut, prompting the sphincter to relieve the pressure. After an animal has digested eaten material, the remains of that material are discharged from its body as waste. Although it is lower in energy than the food from which it is derived, feces may retain a large amount of energy, often 50% of that of the original food. This means that of all food eaten, a significant amount of energy remains for the decomposers of ecosystems. Many organisms feed on feces, from bacteria to fungi to insects such as dung beetles, who can sense odors from long distances. Some may specialize in feces, while others may eat other foods. Feces serve not only as a basic food, but also as a supplement to the usual diet of some animals. This process is known as coprophagia, and occurs in various animal species such as young elephants eating the feces of their mothers to gain essential gut flora, or by other animals such as dogs, rabbits, and monkeys. Feces and urine, which reflect ultraviolet light, are important to raptors such as kestrels, who can see the near ultraviolet and thus find their prey by their middens and territorial markers.