HEP Flury strain of rabies virus was propagated in chick embryo cells under maintenance media of different pH. It was found that viral growth was better and reached a markedly higher maximum titer when the initial pH of maintenance medium was 8.2 to 9.0 than when it was 7.4. The enhancement of viral growth was not ascribable to mere neutralization of acids produced from infected cells, because the different media became almost equally neutral within an early phase of growth curve. Serial passage of the virus in chick embryo cells using pH 8.2 maintenance medium resulted in altered growth characteristics of the progeny virus; first, the virus so passaged could now grow equally well under alkaline and neutral maintenance media, and, secondly, autointerference observable with the parent virus eventually lowered virus yield when neutral maintenance medium was used, but this effect of undiluted passage was eliminated by the use of pH 8.2 maintenance medium.

Herpes virus was reacted with an early rabbit antiserum containing predominantly complementrequiring neutralizing (CRN) antibody to produce CRN-antibody-sensitized virus (SV), and the action of complement (C') upon SV was studied. Reduction of infectivity due to C' was about equal with undiluted and 1000-fold diluted SV. Even higher dilutions which contained about 10 to 100 infectious units per 0.05 ml were also completely inactivated by C'. Kinetic experiments revealed that the velocity of titer reduction in the presence of C' of 100-fold diluted SV was not slower than that of undiluted SV. When SV was first treated with C' and then diluted 100-fold, the surviving virus showed but a slightly reduced efficiency of filtration through the 0.45 p Millipore membrane as compared with SV first diluted 1: 100 and then treated with C'. The titer reduction of SV-C/1 complexes in the presence of C'4 followed a one-hit curve. These results indicated that the reduction of infectivity of SV due to C' was not a result of immunoaggregation of infectious SV. Alternative possible mechanisms of the action of C' are discussed.