Amebiasis is any infection with Entamoeba histolytica. The infection may be limited to the lumen of the intestine and not give rise to any pathological or clinical manifestations, or it may invade the wall of the intestine causing ulceration, and thence spread to the liver, peritoneum, pleura, lung, brain, skin or rarely to other organs. This is one of the most interesting and in some ways baffling infections of man, for several reasons. It is world-wide in distribution. Although most infected persons present no clinical manifestations, others may die from a fulminating infection. Its presence within a given tissue causes lytic necrosis of the tissue, but very little is known about its toxin. The ameba has never been grown in pure culture, for it requires some factor furnished by living bacteria or other cells. Its accurate identification requires skill, experience and sometimes even self-control.