THE HAEMOFLAGELLATES 259 



splenic type, when its occurrence in the circulation is borne in mind. 

 Here, again, Kogers gave the lead. This worker, finding that the parasites 

 developed flagellar stages most readily in an acid medium, suggested (95) 

 that the stomach of some blood-sucking Insect (such as a flea or bug) was 

 probably the place where the above described extra-corporeal phases of 

 the parasite's existence would be found to occur. This has been recently 

 proved to be the case by Patton (93), who has found the Flagellate phases 

 in the bed-bug (Oimex rotundatus [macrocephalus]). It is most probable, 

 therefore, that the infection of human beings is brought about by this 

 Insect, which serves as an alternate host. 



The systematic position and affinities of this parasite have been much 

 discussed. Leishman at first considered the organisms as representing 

 involution-forms of Trypanosomes, being largely influenced by the two 

 chromatin masses ; in this view he was supported by Marchand and 

 Ledingham. Later, he went farther and suggested that they perhaps 

 represented an actual stage in a Trypanosome life -cycle. Laveran and 

 Mesnil, taking more into account the general form and very suggestive 

 binary fission, thought a new species of Piroplasma was concerned, and 

 named the bodies Piroplasma donovani ; in this view Donovan and others 

 have concurred. Other authorities (e.g. Christophers, Ross, and Wright) 

 thought they saw in the parasite an entirely different kind of Sporozoan. 

 Ross called the splenic type Leishmania, and a little later, Wright termed 

 the ulcer- form Helcosoma tropicum. Recently, Rogers has placed the 

 Leishman-Donovan form in the genus Herpetomonas, on account of the 

 similarity in the Flagellate- phase. 



It is probably best to regard the parasites as generically new forms ; 

 in this case the splenic form becomes Leishmania donovani and the ulcer- 

 type, which is most likely a separate species, L. tropica. The organisms 

 are closely related, on the one hand, with the Herpetomouads, and on 

 the other with the Piroplasmata. With regard to the parasites possessing, 

 at some period or other, a trypaniform structure, the complete absence of 

 an undulating-membrane in the cultural forms is no proof that one is not 

 present under certain conditions in Nature. For, as already noted, many 

 Trypanosomes, when " cultivated," may have a very slight indication of 

 a membrane or none at all. Nevertheless, it is by no means improbable 

 that these parasites have remained solely Herpetomonad forms and have 

 not developed the characteristics of a Trypanosome. The fact that the 

 Flagellate-phase is only known to occur in the Invertebrate host, points 

 very strongly to this being the original primary host. In this connection 

 the Herpetomonas lately described by Patton from Culex pipiens (to which 

 reference has been made above) is very interesting, because of the occur- 

 rence of resting- phases resembling the Leishman bodies. Leishmania 

 may well be a similar form which, parasitic in a sanguivorous Insect, 

 has become adapted to the Vertebrate host in its resting, gregariniform 

 phase, and perhaps never develops a trypaniform condition, or even an 

 active flagellar phase therein. Turning to the other side, there can be 

 little doubt that the Piroplasmata are intimately connected with the 

 Leishman-Donovan- Wright bodies. The general agreement of the intra- 

 cellular forms as regards appearance and binary fission has been noted 



