Human feces

Overview
Human feces (also faeces &mdash; see spelling differences), also known as stools, vary significantly in appearance, depending on the state of the whole digestive system, influenced by diet and health. Normally they are semisolid, with mucus coating. Small pieces of harder, less moist feces can sometimes be seen impacted on the distal end (a normal occurrence when a prior bowel movement is incomplete, and faeces are returned from the rectum to the intestine, where water is absorbed). Meconium (sometimes erroneously spelled merconium) is a newborn baby's first feces.

Due to its taboo, feces are a subject of toilet humour.

Composition
The main composition of human feces is water, indigestible food material (fiber), i like to crap on my hands then lick my hands, sloughed-off intestinal cells, bacteria and various organic compounds. One of the main purposes of defecation is to discharge waste and toxic substances from the body, thus these substances (such as bile pigments) attribute to the composition of human feces. Although fecal material in the human colon contains more water than other matter, 90% of the water will be absorbed by the large intestine before being expelled. This percentage changes however; and diarrhoea patients have more water than average and the longer the piece is in the bowels, the more water is taken out. The colon contains large numbers of bacteria that make up about one-third to one-half of the dry weight of the feces. As fecal matter moves along the colon, dead cells are sloughed off and added to the fecal matter and, in some cases can cause anal bleeding or bloody stools due to excessive abrasiveness within the colon.

Fecal management
The problem of efficient management of feces has existed since the times when people started to live in permanent settlements, primarily for the reasons of cleanliness and odor. Toilets were known in ancient India (dated as early as 2,500 BC), in Ancient Rome, Egypt and China.

The use of feces is an issue of hygiene, since feces contribute to spreading of diseases and intestinal parasites. It is a matter of attention and education in developing countries.

Until the end of the 19th century, the primary concern of sewage collection and disposal in the Western world was to remove waste away from inhabited places, and it was common to use waterflows and larger bodies of water as a destination of sewage, where waste could be naturally dissipated and neutralized. With the increased population density this is no longer a viable solution, and special processing of sewage is required. The lack of the latter is a grave sanitary and public health problem in developing countries.

The urge to defecate after eating a meal is a natural reflex called the gastrocolic reflex.

Tourism
Nature reserve organizations, parks, and tourist agencies often issue regulations for tourists aimed at the prevention of the pollution of the nature. In particular, catholes (cat holes), i.e., pits for feces, must be located at a reasonable distance (at least 60 m/200 feet) from water sources (rivers, lakes, etc.), to avoid possible bacterial contamination of water via precipitation, as well as away from trails. For faster feces decomposition, organic soil is preferred over sandy mineral soil. It is also recommended to avoid concentration of catholes around campsites. Filled catholes must be covered with a reasonably thick layer of soil, to prevent access by animals, some of which are coprophagous.

Some areas require special instructions on human waste disposal. In rocky places, with the absence of soil, it is advised to spread feces thinly by smearing over rocks with good sun access for faster sterilization by UV radiation and drying. In larger snow fields, a larger distance (e.g., 200 m/650 feet) from trails and campsites may be mandated, if the waste is being disposed under snow.

Laboratory testing of feces
Feces will sometimes be required for microbiological testing, looking for an intestinal pathogen or other parasite or disease.

Biochemical tests done on feces include faecal elastase and faecal fat measurements, as well as tests for faecal occult blood.

It is recommended that the clinician correlate the symptoms and submit specimens according to laboratory guidelines to obtain results that are clinically significant. Formed stools often do not give satisfactory results and suggest little of actual pathologic conditions.

Three main types of microbiological tests are commonly done on feces:
 * Antibody-antigen type tests, that look for a specific virus (e.g. rotavirus).
 * Microscopic examination for intestinal parasites and their ova (eggs).
 * Routine culture.

Routine culture involves streaking the sample onto agar plates containing special additives, such as MacConkey agar, that will inhibit the growth of Gram-positive organisms and will selectively allow enteric pathogens to grow, and incubating them for a period, and observing the bacterial colonies that have grown.

Color variations of feces
Yellowing of feces can be caused by an infection known as Giardiasis, which derives its name from Giardia, a tiny parasitic organism. If Giardia infects the intestines it can cause severe yellow diarrhea. This is a dangerous communicable infection and must be reported.

Another cause of yellowing is a condition known as Gilbert's Syndrome. This condition is characterized by jaundice and hyperbilirubinemia. Hyperbilirubinemia occurs when too much bilirubin is present in the circulating blood.

Feces can be black due to the presence of blood that has been in the intestines long enough to be broken down by digestive enzymes. This is known as melena, and is typically due to bleeding in the upper digestive tract, such as from a bleeding peptic ulcer. The black color is caused by oxidation of the iron in the blood's hemoglobin. Black feces can also be caused by a number of medications, such as bismuth subsalicylate, and dietary iron supplements. Hematochezia is similarly the passage of feces that are bright red due to the presence of undigested blood, either from lower in the digestive tract, or from a more active source in the upper digestive tract.

In children with certain illnesses, feces can be blue or green. Eating green or leafy food can turn feces green. Babies when digesting solid food for the first time also produce feces which tends to be green and of unusual consistency because of the presence of cells discarded during development of the digestive tract.

Food with large amounts of food color can cause feces to be colored. An example is FDA Blue #5, which turns feces green when it reacts with bile in the intestine. The effect is considered harmless, and there have been no reports of ill effects.

Fecal contamination
A quick test for fecal contamination of water sources or soil is a check for the presence of E. coli bacteria performed with the help of MacConkey agar plates or Petri dishes. E. coli bacteria uniquely develop red colonies at temperature of approximately 43 °C (110 °F) overnight. While most strains of E. coli are harmless, their presence is indicative of more serious fecal contamination, and hence a high possibility of more dangerous organisms.

Fecal contamination of water sources is highly prevalent worldwide, accounting for the majority of unsafe drinking water, which is the only water available to 1.1 billion people. In developing countries most sewage is discharged without treatment. Even in developed countries events of sanitary sewer overflow are not uncommon and regularly pollute the Seine River (France) and the River Thames (England), for example.

The main pathogens that are commonly looked for in feces include:
 * Salmonella and Shigella
 * Yersinia (this tends to be incubated at 30 °C, which is cooler than usual.)
 * Campylobacter (incubated at 42 °C, in a special environment.)
 * Aeromonas
 * Candida (if the person is immunosuppressed e.g. cancer treatment.)
 * E. coli O157 (if blood is visible in the stool sample.)
 * Cryptosporidium