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could support the development of a few epimastigote forms in the procyclic
populations.
A cell-free culture system that allows direct adaptation for bloodstream
forms into procyclics has been devised in Dr. B r u n's laboratory.
The liquid medium contains Eagle's MEM with Earle's salts, hemin,
and foetal bovine serum. The procyclics reached a maximum concentration
of 4-5 X 10 7 /ml.
So far, continuous cultivation of mammalian infective stages of
T. congolense has not been possible using the methods applied to T. brucei
sspp. However, the following important advances have provided optimism
in this field. The observations of Luckins and Gray (1978)
of the close association of T. congolense with collagen fibrils in the local
reactions ait the sites of bites of infected tsetse flies suggested that
this material might serve as a useful source of trypanosomes for in
vitro studies. Indeed, T. congolense in cultures prepared from bovine
dermal explants taken from local reactions and incubated at 37°C retained
their infectivity for up to 21 days (Gray et al. 1979). More
satisfactory results were obtained using two unrelated stocks of T. congolense
established in cultures at 28°C with trypanosomes from proboscides
of infected tsetse flies placed beside bovine dermal collagen explants
(Gray et al. 1981). The trypanosomes multiplied and formed
an adherent layer in the culture flasks. They were subpassaged in medium
without dermal explants and retained their infectivity for several
months. Infectivity titrations indicated an output of over 10 6 infective
organisms per 25 cm 2 culture flask in a 2-day period. The trypanosomes
resembled those in the hypopharynx and labrum of a tsetse
fly-
(3) Trypanosoma vivax
The relatively little attention given to the cultivation of T. vivax
may be due to the problems of working with this species outside Africa.
The first successful attempts to cultivate infective forms were reported
by Trag er (1959). He found that bloodstream forms from infected
sheep added to cultures of organs of Glossina palpalis transformed into
the various stages found in the vector. Some samples of two culture
lines grown for several weeks, and exposed to an elevated temperature
of 38 c C, developed infections in sheep. During a subsequent visit to
the laboratory in Nigeria, Trager (1975) obtained the development and
multiplication of epimastigote forms in similar tsetse fly tissue cultures
but using a different medium. Older cultures were reported to contain
transitional forms almost resembling metacyclic trypanosomes.
During a recent visit to ILRAD in Kenya, Dr. Brun, in collabora-
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