[Illustration: FIG. 49.--_a_, _Herpetomonas_; _b_, _Crithidia_; _c_, _Trypanosoma_. (After Porter.)] Laveran and Franchini (1913–14)[119] have recently succeeded in inoculating _Herpetomonas ctenocephali_, from the gut of the dog flea, intraperitoneally into white mice, and producing an experimental leishmaniasis in the mice. A dog was also infected. They have also succeeded in infecting mice with _H. pattoni_--a natural flagellate of the rat flea--by mixing infected rat fleas with the food of the mice, and by causing them to ingest infected fæces of rat fleas. Further, they have shown that infection with the herpetomonas occurs naturally by this method, that is, by the rodents eating the fleas and not by the insects inoculating the flagellates into the vertebrates when sucking blood. These experiments shed an interesting light on the probable origin of _Leishmania_ and its cultural herpetomonad stage, which were very probably once parasitic flagellates in the gut of an insect. [119] _C. R. Acad. Sci._, clvii, pp. 423, 744. _Ibid._, clviii, pp. 450, 770. _Bull. Soc. Path. Exot._, vii, 605. Fantham and Porter[120] (1914–15) have shown that young mice may be inoculated or fed with _Herpetomonas jaculum_, from the gut of the Hemipteran, _Nepa cinerea_ (the so-called “water-scorpion”), with fatal results. The pathogenic effects are like those of kala-azar. They also showed that the post-flagellate stages of the herpetomonads seemed most capable of developing in the vertebrate. [120] _Proc. Camb. Philosoph. Soc._, xviii, p. 39. A herpetomonad, _H. davidi_, has been found in the latex of species of the plant-genus _Euphorbia_ in Mauritius, India, Portugal, etc. It is apparently transmitted to the plants by _Hemiptera_. The plants sometimes suffer from “flagellosis.” Franchini (1913)[121] has described a new parasite, _Hæmocystozoon brasiliense_, from the blood of a man who had lived in Brazil for many years. It possesses flagellate and rounded stages, and is closely allied to the herpetomonads. [121] _Bull. Soc. Path. Exot._, vi, pp. 156, 333, 377. Genus. *Crithidia*, Léger, 1902, emend. Patton, 1908. _Crithidia_ is the generic name of vermiform flagellates with a central nucleus, a blepharoplast or kinetic nucleus in the neighbourhood of the principal nucleus, and a rudimentary undulating membrane bordered by a flagellum arising from a basal granule, which is the centrosome of the kinetic nucleus (fig. 49_b_). The anterior or flagellar end of the body is attenuated and fades off as the undulating membrane.