SCHIZOGONY OF TRYPANOSOMA EVANSI. 57 



in paraffine sections. These preparations have been stained 

 with Giemsa's stain, aqueous alum hematoxylin, Mallory's ferric 

 choloride hematoxylin, and Seidlin's iron hematoxylin. Air- 

 dried smears of both the blood and organs, stained twelve to 

 twenty-four hours with Giemsa's stain, have given the best 

 results. The sections of the organs have been useful in de- 

 termining the relation of the stages of development of the tryp- 

 anosome to the tissues. 



Tnjpanosoma evansi, when inoculated subcutaneously into 

 guinea pigs, has an incubation period that varies from five to 

 seventeen days, depending upon the strain of the virus, the num- 

 ber of trypanosomes inoculated, and the susceptibility of the 

 animal. The disease runs a more or less chronic course in these 

 animals, usually of from one to several months' duration. The 

 course of the disease is marked by alternating phases of increase 

 and decrease of the parasites in the peripheral blood. The 

 trypanosomes will increase to a maximum and often swarm in 

 the blood for several days; they will then decrease, and may 

 wholly disappear from the peripheral circulation for several 

 days, only to reappear and repeat the cycle. Sometimes one 

 or more smaller crests of multiplication will intervene between, 

 two larger crests. Occasionally the infected guinea pig will die 

 at the summit of the first crest of multiplication of the parasites 

 in its blood. 



Guinea pigs have been killed at different periods in the mul- 

 tiplication curve of the parasites in the blood and preparations 

 from the different internal organs examined. It has been found, 

 corresponding to the observations of Salvin-Moore and Breinl 

 on Trypanosoma gambiense and of Fantham on Trypanosoma 

 gambiense and Trypanosoma rliodesiense, that at or near the 

 maximum of the increase of the trypanosomes in the blood large 

 numbers of round, binucleate bodies are developed in certain 

 of the internal organs. Guinea pigs inoculated intraperitoneally 

 and killed from the fifth to eighth day, according to the directions 

 of Chagas for finding the schizonts in Schizotrypaniim criizi and 

 followed by Buchanan in studying the development of Trypano- 

 soma brucei (pecandi) in the internal organs of the gerbil, 

 showed only a few of the round forms. Guinea pigs, killed 

 during the decrease or the absence of the trypanosomes from the 

 peripheral blood, showed few or no round forms in the organs. 



The place of development of these round forms of Trypano- 

 soma evansi does not correspond to that of the development of 

 the "latent bodies" Trypanosoma gambiense and Trypanosoma 



