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Jennerlan prophylaxis in man by means of intradermal inoculation of cultured vaccine virus was described (1) in 1935. Since then this type of prophylaxis against smallpox has been used by us, by many private physicians, and by physicians in a number of clinics. For the last 3 years the virus employed has been from generations 30 to 170 of the "second revived" strain of cultured vaccine virus, dried ]From the frozen state in the presence of gum acacia and sealed in vacuo (1, 2). This strain (3) was originally derived from calf lymph vaccine virus supplied by the New York City Board of Health in 1931 and has been propagated since then by serial transfers in a medium consisting of Tyrode's solution and minced chick embryo tissue. Intradermal inoculation of the virus in rabbits reveals that it maintains a uniform potency during continued cultivation. Moreover, the lesions produced in rabbits are less severe than are those caused by other strains of vaccine virus.When inoculated intradermally in susceptible persons, cultured vaccine virus produces a high percentage of positive reactions. The percentages reported by those to whom the virus has been dispensed have ranged from 80 to 100; it is probable that an average of over 90 per cent has been obtained in a minimum of 6000 to 7000 intradermal vaccinations. In our experience with more than 200 primary vaccinations the incidence of "takes" has been 100 per cent. Typical positive reactions appear as small red papules on the 4th to 9th day after inoculation. Erythema and induration increase until the lesions are 2 to 4 cm. in diameter at their height 4 to 6 days later. Erythema disappears rapidly although induration may persist 4 or 6 weeks. If

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