406 FAMILY: TKYPANOSOMID^ 



which occurs with the serum of kala azar cases. If one part of serum 

 is mixed with two parts of distilled water, an opacity is produced. If 

 the water is poured on the surface of the serum, a ring effect is obtained. 

 The test has been elaborated into a quantitive one by Bramachari and 

 Sen (1923). 



Wagener (1923) has shown that the injection of alkaline extracts of 

 Leishmania from cultures into the skin of rabbits previously rendered 

 sensitive by injections of cultural forms of Leishmania produces a local 

 reaction in the form of an erythematous papule, which reaches its height 

 in forty-eight hours, and persists from three to five days. The antigen 

 can be prepared from both L. tropica and L. donovani, as it is not specific 

 for either parasite. If these results are confirmed, the reaction may be 

 of use for diagnostic purposes. The serological observations made by 

 Noguchi (1924) have been referred to above (p. 399). 



MORPHOLOGY. — The parasite Leishmania donovani, which is morpho- 

 logically indistinguishable from L. tropica, is a small organism usually 

 circular or oval in outline (Plate IV., 7-10, p. 406). It consists of a mass of 

 cytoplasm covered by a definite membrane. The cytoplasm contains 

 two very characteristic structures, the recognition of which is essential 

 to the identification of the organism. One is the nucleus, and the other 

 the kinetoplast. The former is a more or less spherical body, with a 

 diameter about one-third to a half of the shortest diameter of the organism. 

 It usually lies against the membrane, and is somewhat flattened on this 

 side. The flattening may be so marked that its form is reduced to that 

 of a hemisphere, or even of a thin disc, so that in optical section it is seen 

 as a semicircle or merely a narrow structure lying along one side of the 

 parasite. The extreme flattening of the nucleus often appears to be 

 intensified by the presence of one or more vacuoles in the cytoplasm, 

 which may be so large as to reduce the parasite to the condition of a thin- 

 walled sac. The second structure of importance is the kinetoplast, which 

 is usually seen as a rod lying with its long axis directed towards the nucleus. 

 In preparations it may appear as a small spherical body, but in most cases 

 this is due to its long axis being perpendicular to the slide. In ordinary 

 dried films stained by the Romanowsky method, the nucleus appears as a 

 mass of bright red granules, while the kinetoplast, which is a more solid com- 

 pact body, takes a deep reddish-purple tint. In deeply stained parasites 

 a red line, first described by Christophers (1904), can be traced from the 

 blepharoplast, which lies near the centre of the kinetoplast, to the surface 

 of the parasite. This is the axoneme, which gives rise to the flagellum 

 of the leptomonas forms which develop in cultures (Plate IV., 6, p. 406). 

 The size of the parasite varies considerably. When spherical, it measures 

 from 1 to 3 microns in diameter. More usually it is ovoid, with the long 



