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220 According to Hirsch, in the tropics this form of ulceration is especially prevalent about the commencement of the cool season; in more temperate climates, towards the end of summer or beginning of autumn. Years of prevalence may be succeeded by years of comparative rarity; possibly in harmony with altered sanitary conditions. In Delhi, for example, in 1864 from 40 to 70 per cent, of the resident Europeans were affected with the local sore; on certain sanitary improvements being effected, the frequency of the disease was immediately materially reduced.

Histology; etiology.—— Section of the papule displays an infiltration of the derma by a mass of small round granulation cells. These lie between the elements of the tissues, particularly about blood-vessels, lymphatics, and sweat-glands; towards the centre of the lesion they completely replace the normal structures. Various micro-organisms have been described in association with oriental sore. By staining sections in gentian violet and afterwards partly decolorizing in spirit, Cunningham and Firth found certain violet-stained bodies (Helcosoma tropicum), varying in size and grouping, in a proportion of the infiltrating cells. These bodies Cunningham was inclined to regard as parasites. Riehl looked upon them as the result of a hyaline degeneration of protoplasm, and advanced a claim for certain micrococci which he said he found in great profusion in the granulation cells. That Cunningham's view is correct was proved by an American observer, H. Wright, who, in 1903, found in the granulation cells of an oriental sore the Leishman body (Cunningham's parasites) in gi-eat profusion. This observation has been abundantly confirmed in India and elsewhere; so that it may now be considered as definitely established that the cause of oriental sore is the Leishman body, or a body morphologically identical with this parasite. For the characters of the Leishman body, see p. 208 and Plate V.

The cultivation of the parasite, first carried out by Nicolle, is easily effected in the N.N.N. medium.