=Definition.=—Under this designation we group three diseases, two of which are general infections and one a cutaneous affection. It is now thought that the visceral leishmaniasis of adults or Indian kala-azar and that of young children or infantile kala-azar are one and the same disease. The cutaneous leishmaniasis of the Near East or oriental sore and the various leishmania ulcerations of tropical America are grouped with the others solely by reason of their cause, this being a protozoon of the same genus, _Leishmania tropica_ for the skin leishmaniases, and _L. donovani_ for the visceral ones. Most authorities assign to infantile kala-azar a distinct species, _L. infantum_. The visceral leishmaniases are characterized by a chronic course, marked splenic enlargement, progressive anaemia and emaciation together with leucopenia. The cutaneous leishmaniases can only surely be differentiated from other tropical sores by the finding of the leishman bodies from smears made from the granulomatous tissue of the sore. =Synonyms.=—Dum-Dum Fever, Tropical Splenomegaly (for Indian Kala-azar), Splenic Anaemia of Infants, Ponos (for infantile kala-azar), Oriental Sore, Biskra Button, Bagdad Boil, Bouton d’Orient, Aleppo Boil, Granuloma Endemicum (for the Eastern cutaneous leishmaniasis), Espundia, Bubas Braziliana, Uta, Forest Yaws (for the American cutaneous leishmaniasis). GENERAL CONSIDERATIONS OF HISTORY, ETIOLOGY AND RELATIONSHIP =History.=—In 1869 the English medical authorities in India became familiar with a very fatal disease among the natives of Assam but regarded it as a very malignant form of malaria. The native designation for the disease was kala-azar. In 1889 Giles investigated this disease and finding hookworm ova in almost all of the cases he came to the conclusion that it was ancylostomiasis. Rogers (1896) and Ross (1898) after studying the disease were of the opinion that it had to do with malaria, the former regarding it as a malignant form of malaria and the latter that it was malaria plus some secondary infection. Owing to the very similar temperature charts and misled by agglutination tests of the serum of kala-azar patients, which he regarded as showing agglutinins for the _Micrococcus melitensis_, Bently, in 1902, claimed that kala-azar was a malignant form of Malta fever. In 1903 Manson suggested that the disease might be caused by a trypanosome, the absence of malarial parasites and non-response to quinine being against the then usually accepted malarial etiology.