In cultures the various species of _Leishmania_ all grow into herpetomonad, uniflagellate organisms (fig. 50, 10), about 12 µ to 20 µ in body length. On this account Rogers[125] and Patton place the Leishman-Donovan body within the genus _Herpetomonas_. The method of culture may be used in diagnosing leishmaniases. [125] _Proc. Roy. Soc._, B, lxxvii, p. 284. Kala-azar is very probably an insect-borne disease. Patton[126] suspects the bed-bug to be the transmitter and finds (fig. 50, _4_-_6_) that the Leishman-Donovan body can develop into the flagellate stage in the digestive tract of the bed-bug. Feeding experiments are unsatisfactory, since there are very few cases in which the parasites occur in sufficient numbers in the peripheral blood to make the infection of the insect possible, or at any rate easy. In examining the alimentary tracts of insects for possible flagellate stages of _Leishmania_, it must be remembered that in many insects natural flagellate parasites, belonging to the genus _Herpetomonas_, may occur therein; such natural insect flagellates may be harmless, and have no connection with the life-cycle of _L. donovani_. Natural herpetomonads are known to occur in the alimentary tracts of flies, mosquitoes, sand-flies, fleas and lice, but not in bed-bugs. Further, if such flagellates are able to be inoculated into and live within vertebrate hosts, producing symptoms like those of leishmaniasis, the origin of kala-azar is indicated (see pp. 104, 112). [126] _Sci. Mem. Govt. India_, Nos. 27, 31 (1907–08). *Leishmania tropica*, Wright, 1903. Syn.: _Helcosoma tropicum_, Wright, 1903; _L. wrighti_, Nicolle, 1908; _Ovoplasma orientale_, Marzinowsky and Bogrow. It is believed by some that the parasite was first described by Cunningham in 1885, and studied by Firth in 1891, being called by him _Sporozoon furunculosum_. If these earlier studies were of the parasite, then its correct name is _L. furunculosa_, Firth, 1891. The benign disease produced by this parasite has received many names, among the best known being Oriental sore, Tropical sore, Delhi boil and Aleppo button. These names, however, are not happy ones, as cutaneous leishmaniasis (_e.g._, on the ear) is now known to occur in the New World, for example in Mexico, Venezuela, Brazil and neighbouring States. However, it may be necessary to subdivide cutaneous leishmaniases later. In the Old World the disease occurs in India, Persia, Arabia and Transcaucasia. It is also known in Algeria, Northern Nigeria, Egypt, Sudan, Crete, Calabria, Sicily and Greece.