[In vitro fusion ability of agents causing slow diseases of the central nervous system].

The authors study cell fusion in vitro induced by two kinds of slow viruses : visna virus of sheep and scrapie of mouse and Creutzfeldt-Jakob disease of man agents. Cell-fusion induced by visna virus is either slow and late occuring (fusion from within) or early and rapid (fusion from without) according to experimental conditions. Whereas, cell-fusion induced by spongiform encephalopathies agents is only of slow appearance, looking an endogenous phenomenon.