SCHIZOGONY OF TRYPANOSOMA EVANSI. 61 



multiply by simple division in the gut of the invertebrate host 

 {Conorhinus megistus) and in cultures on Novy and McNeal's 

 medium, a suspicion is raised of the accuracy of the observation 

 that it is absent in the peripheral blood of the vertebrate host. 



The significance of this schizogony in the life-cycle of the tryp- 

 anosome is uncertain. Fantham as well as Salvin-Moore and 

 Breinl consider the round form of Trypanosoma (jambiense and 

 Trypanosoma rhodesiense to be a resistant stage of the parasite 

 which persists during the latent phase of trypanosomiasis when 

 the parasites are absent from the peripheral blood. Salvin- 

 Moore and Breinl designate them as such by the name "latent 

 bodies," and Fantham suggests, although he does not definitely 

 state, that these latent bodies may be resistant to drugs used 

 in the treatment of trypanosomiasis and may be responsible for 

 the relapses that occur after chemotherapeutic treatment. If 

 these so-called latent bodies are, as my observations have in- 

 dicated, only an early stage in the development of the schizonts, 

 it would seem more probable that the mature schizocysts might 

 be the resistant stage of the trypanosome. However, an ex- 

 amination of the spleen and other internal organs of guinea pigs 

 killed during the decrease of the trypanosomes in the blood, or 

 during the latent phase of the infection, has shown no schizocysts 

 but only a very few flagellated trypanosomes and round forms 

 (schizonts). It is possible, therefore, that some of the young 

 schizonts persist through the latent period and undergo schizog- 

 ony at the beginning of the relapse, giving rise to the new 

 generation of trypanosomes. It is also possible that it is un- 

 necessary to assume the existence of a special resistant stage of 

 the trypanosome to account for latency and relapse in trypano- 

 somiasis. Further morphological and experimental investiga- 

 tion is necessary to decide those questions. 



CONCLUSIONS. 



In the developmental cycle of Trypanosoma evansi a schizog- 

 ony takes place in the spleen of the vertebrate host. 



The observations of Salvin-Moore and Breinl, Fantham, and 

 Buchanan that forms similar to the young schizonts of Trypano- 

 soma evansi occur in the internal organs of animals infected 

 with Trypanosoma gambiense, T. rhodesiense, and T. brucei 

 make it probable that schizogony is a reproductive process 

 common to the trypan osomata. 



The validity of Schizotrypanum Chagas as a genus distinct 

 from Trypanosoma Gruby appears to be doubtful. 



