688 SCIENCE PROGRESS 



of one race that had become resistant to pyronin, the kineto- 

 nucleus was absent from every trypanosome, although both 

 tropho-nucleus and kineto-nucleus were present and showed 

 no abnormal features in the original race of T. brucei from 

 which this pyronin-resistant race had been produced. 



Werbitski then injected the original race of T. brucei into 

 a mouse and when its blood was swarming with parasites 

 injected a maximum dose of pyronin. On the following day 

 40 to 60 per cent, of the trypanosomes were without a kineto- 

 nucleus. The next day their number was less and on inocu- 

 lating this race into another mouse the trypanosomes without 

 kineto-nuclei rapidly diminished and in the case of a third 

 animal completely disappeared. It was found by experiment 

 that the " mono-nuclear " trypanosomes were less resistant than 

 the normal " bi-nuclear " forms and that in consequence they 

 were crowded out by the latter. It was then found that 

 substances other than pyronin possessed this property of 

 causing the disappearance of the kineto-nucleus, e.g. repre- 

 sentatives of the oxazine series and especially orthoquinonoid 

 substances. 



Certain preparations of oxazine, given in doses of y^Vtt to 

 won of the body-weight of the infected mouse, caused 80 to 

 90 per cent, of the trypanosomes to lose their kineto-nuclei 

 within twenty-four hours. This race was passed through ten 

 mice in succession, an injection of oxazine being given in each 

 case ; at the end of this treatment it was found that the kineto- 

 nuclei had disappeared from all the trypanosomes. This race 

 of mono-nuclear trypanosomes maintained its peculiarity through 

 several generations, although none of the animal hosts through 

 which it was passed were treated with any drug. 



The mono-nuclear trypanosomes do not differ in any other 

 respect from the ordinary bi-nuclear forms from which they 

 have been derived. In both races the same variations occur in 

 the shape of the parasites — such as the long and narrow, short 

 and broad, division forms, etc. The flagellum, in both cases 

 ends in a small club-shaped thickening known as the end-bead, 

 which is considered by Prowazek to be the equivalent of the 

 centriole. This end-bead is usually situated in close relation to 

 the kineto-nucleus and the latter is commonly supposed to 

 control the movements of the flagellum through the end-bead. 

 There is no difference in motility, however, between the mono- 



