Published online by Cambridge University Press: 15 May 2009
Tr. Lewisi has been cultivated by me for nine generations, the duration of cultivation extending over a period of nine months. The culture is still alive and is now in its tenth generation. A culture of Tr. Brucei was cultivated through three generations for a period slightly exceeding eighty days. These cultural experiments, however, in no way compare, in duration of time, with those of Novy and McNeal, who have cultivated Tr. Lewisi through twenty-six generations in two years, and Tr. Brucei through twenty-seven generations in eight months. Nagana trypanosomes degenerate rapidly in cultures and then become non-virulent, but a culture of Tr. Lewisi retains its infectivity for rats for a long period. From the study of well stained preparations it has been found that the cultural forms of the rat trypanosome differ considerably from those of the adult parasite found in the blood. The chief points of difference are: (1) The trypanosome is exceedingly motile and is generally spindle-shaped. (2) The centrosome is placed anteriorly. (3) The flagellum is very long and active and has but a short intracellular course, in consequence of the position of the centrosome, from which it arises. (4) No undulating membrane is apparent. (5) The trypanosomes form colonies, which ultimately contain many thousands of individuals. The flagella of the latter are directed centrally. In rats, infected with cultures of Tr. Lewisi, the usual forms of parasite appear. The cultural forms of Tr. Brucei resemble the trypanosomes found in the blood, but are more active. The chief points of difference, viz. development of two or more vacuoles and numerous granules and sometimes the breaking up of the chromatin of the nucleus, are probably due to degeneration. The colonies, found in cultures of Tr. Brucei, consist of a comparatively small number of trypanosomes, which are arranged irregularly or with their flagella directed peripherally. The differences between cultures of Tr. Lewisi and Tr. Brucei are summarised on page 43.