In 1950, Tobie et al. described a diphasic blood agar medium that supported the cultivation of proventricular forms of the human sleeping sickness parasites, Trypanosoma brucei rhodesiense and T. b. gambiense, which was a major advance over similar systems used by other investigators. First, rabbit blood was used in place of human blood in preparation of the diphasic blood agar. Second, the culture system supported the differentiation of bloodstream-form trypanosomes, which could not at that time be cultured in vitro, into proventricular tsetse forms, which could be cultured. This provided the opportunity for controlled investigations of these parasites. Third, the trypanosomes grew to a high density, yielding about 2 × 107 organisms per milliliter, an adequate number for biochemical analysis of the cultured organisms. Tobie et al. (1950) exploited the system to carry out quantitative studies on sugar utilization by the parasites. They...

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