THE H^MOFLAGELLATES AND ALLIED FORMS 319 



claims to have transmitted L. infanium by fleas. In the case of L. tropica, 

 Wenyon points out that the sores occur almost invariably on parts of the 

 person not covered or protected by clothing, a fact which is strongly against 

 the infection being effected by fleas, bugs, or ticks, and indicates that the 

 invertebrate host is some biting fly, probably either a species of mosquito or 

 a sand-fly (Phlebotomus). Experimental evidence of transmission, however, 

 is as yet lacking. 



It is clear from the development that the species of Leishmania are non- 

 flagellated phases of a true leptomonad, and it has been proposed by Rogers 

 to abolish the genus Leishmania, and to place the parasites in question in the 

 genus Herpetomonas. The life-cycle of a Leishmania is, however, so different 

 from that of a typical Herpetomonas (Leptomonas), which is parasitic solely 

 in the digestive tract of an insect, that the genus Leishmania may well be 

 allowed to stand. 



So long as the development is only known from artificial cultures, the 

 significance of the " spirillar " forms of Leishman cannot be determined. 

 Assuming that they are not merely degenerative forms, they may possibly 

 represent the propagative stage in which the invertebrate host inoculates 

 the parasite back into the vertebrate ; the fact that L. donovani causes a sys- 

 temic disease rather suggests that the initial phase in the vertebrate may be 

 a flagellated form which is carried all over the body in the circulation, and 

 from which the typical Leishmania-phase is developed. Another possible 

 explanation of the spirillar forms is that they may be gametes, perhaps of 

 male sex ; but there is no evidence in support of this interpretation either 

 from observation or analogy, since sexual phenomena in leptomonads have 

 not been observed. Marzinowsky claims, however, to have observed copula- 

 tion of male and female gametes in cultures of L. tropica. 



Darling has described under the name Histoplasma capsulatum an organism 

 causing a disease in human beings, and believed to be allied to Leishmania. 

 It is stated to develop flagellated phases in lung-smears. For Toxoplasma, 

 referred by some to a position near Leishmania, see p. 387. " Leucocytozoon " 

 piroplasmoides, found in epizootic lymphangitis of horses in Senegal (Thiroux 

 and Teppaz), is possibly a Leishmania, but only a single mass of chromatin 

 appears to be present in the body, and no flagellated forms were obtained 

 in cultures ; possibly, therefore, its proper systematic position is near Toxo" 

 plasma. 



VI. THE GENUS PBOWAZEKIA. 



This genus was created by Hartmann and Chagas (62) for P. cruzi, a species 

 discovered in a culture from human faeces on an agar-plate in Brazil. Two 

 other species have also been described from human faeces namely, P. wein- 

 bergi, Mathis and Leger (Fig. 141, A and B), and P. asiatica, Whitmore. 

 It would appear, therefore, that several species (or possibly a single species) of 

 this genus occur in various parts of the world in human faeces. Martini considers 

 P. cruzi to be a cause of human diarrhoea and intestinal catarrh in China. 

 Nagler has described a species P. parva (Fig. 141, C), which is free-living, and 

 Dunkerly has found a Prowazekia in the gut of the house-fly. The form which 

 Walker has described under the name " Trypanoplasma ranee " very possibly 

 should be referred to Prowazekia ; it was obtained from cultures of the 

 intestinal contents of the frog. 



In its structure, Prowazekia resembles the genus Bodo in the heteromastigote 

 arrangement of the flagella, and in its nuclear apparatus it resembles Trypano- 

 plasma, with trophonucleus and kinetonucleus. It differs structurally from 

 Trypanoplasma only in the fact that the backwardly-directed flagellum is free 

 from the body, not united to it by an undulating membrane ; it bears, in fact, 

 the same structural relation to this genus that Trichomastix has to Trichomonas. 

 Alexeieff (388) denies that the genus is distinct from Bodo, and considers that 

 the name Prowazekia should be cancelled ; he identifies P. cruzi with B. edar, 

 Klebs, and P. parva with B. saltans, Ehrenberg. 



