“…E Miller et al, 1980;Caignard et al, 1985;Newcomb et al, 1978) by mechanisms invoking host immtune involvement (B.E. Miller et al, 1980;Caignard et al, 1985;Newcomb et al, 1978) and by mechanisms not involving host immunity . Interactions in which the growth of a sister subpopulation is enhanced, have also been described (Caignard et al, 1985;Brodt et al, 1985;Butler et al, 1983;Tofilon et al, 1984), as well as, in some instances, the tendency for two subpopulations to form a particular final ratio (Leith et al, 1985;Jansson & Revesz, 1976).…”