The boils often occur on the face, and before ulceration the parasites may be found in the cells at the margin and floor of the “button.” In searching for parasites the scab should be removed and scrapings made from the floor and edges. Where lesions occur atrophy of the epidermis takes place, and infiltration of mononuclear cells (_e.g._, plasma cells, lymphoid and endothelial cells) follows. The parasites are intracellular, being found inside mononuclear cells. In non-ulcerating sores, Cardamitis found some free parasites. Non-ulcerating forms are said to occur in the Sudan. In the Old World the sores are often limited to exposed surfaces of the body. Infection of mucous membranes (such as the lip, palate, buccal and nasal membranes) may occur, especially in South America, and are often known there as “Espundia.” Christopherson (1914) has recorded a case in Khartoum. _Leishmania tropica_ is equally well cultivated on Novy-MacNeal-Nicolle medium or on citrated blood. The usual temperature for cultivation is 22° to 28° C., though Marzinowski claims to have cultivated the parasite at 37° C. _L. tropica_ can be inoculated into monkeys and dogs, with the production of local lesions. Material from a human sore or flagellates from a culture may be thus successfully inoculated. Also infected material may be rubbed directly into a scarified surface. The incubation period is long, extending over several months. The duration of the disease may be from twelve to eighteen months. Recovery from one attack of tropical sore confers immunity, and the Jews in Bagdad inoculate their children with the disease on a part of the body which will be covered, and so secure immunity in adult life. The mode of transmission of _L. tropica_ is unknown. Wenyon (1911)[127] has found that the parasite develops into the flagellate stage in the digestive tract of _Stegomyia fasciata_ in Bagdad. Patton (1912)[128] has found similar development in the bed-bug in Cambay. The house-fly, _Phlebotomus_ and _Simulium_ have been suspected as transmitters in different parts of the world. [127] _Parasitology_, iv, p. 387. [128] _Sci. Mem. Govt. India_, No. 50. An interesting announcement has been made recently (May, 1913), that Neligan has found that _L. tropica_ occurs in dogs in Teheran, Persia, producing ulcers on the dogs’ faces (_cf._ natural occurrence of _L. infantum_ in dogs--see p. 110). Yakimoff and Schokhor (1914),[129] have found the disease in dogs in Tashkent. [129] _Bull. Soc. Path. Exot._, vii, p. 186.