Many toxic plants are unpalatable, so animals avoid them where possible. However, this is not always the case; locoweeds, for example, are addictive and once a horse has eaten them, it will continue to eat them whenever possible, and can never be exposed to them again.
Micrograph of melanosis coli, with the characteristic mucosal lipofuscin-laden macrophages (brown). Melanosis coli, also pseudomelanosis coli, is a disorder of pigmentation of the wall of the colon, often identified at the time of colonoscopy.It is benign, and may have no significant correlation with disease. The brown pigment is lipofuscin in macrophages, not melanin.urther information: Factitious diarrhea. The most common cause of melanosis coli is the extended use of laxatives, and commonly anthraquinone containing laxatives such as Senna and other plant glycosides.
Though the specific cause of acral lentiginous melanoma is unknown, it's thought that melanoma develops when there are problems with the DNA that controls certain skin cells. In people with acral lentiginous melanoma, DNA is damaged and causes an overgrowth of the skin cells that produce skin pigment.