Our studies on rabies vaccines thus far have led us to the view that in order to develop and test vaccines, quantitative methods are necessary, and that such quantitative methods may be exploited to greatest advantage by using mice, preferably W-Swiss, as the test animal. Dogs, due to their variability and susceptibility to intercurrent infections when kept under experimental conditions, are useful chiefly to check whether or not a vaccine produces a high grade of immunity; they remain of limited value in testing the comparative potencies of weak vaccines. A second point is that the Pasteur strain of virus has proved as potent as any tested for the preparation of vaccines. Another point is that virus material for preparing vaccines must titre at least 330,000 mouse doses per cc. to be effective. This requirement has eliminated all culture vaccines thus far reported, with the possible exception of Plotz's (7) and leaves virus-containing brain tissue as the sole potent source of vaccine.

In summary, we believe that a single injection of non-virulent irradiated vaccine, prepared as herein described, immunizes mice and dogs effectively against a subsequent test inoculation of virulent rabies virus and does so to a greater degree than do other vaccines now obtainable. It is easily and quickly prepared, keeps well, and has a low nitrogen content.

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