A new species of Haemophilus, Haemophilus vaginalis, has recently been incriminated as the cause of human non-specific vaginitis and urethritis. A very similar if not identical organism obtained from the same sources is the subject of this report. The name H. vaginalis is accepted for it. A systematic description of this organism is given, including microscopic and colonial appearances, nutritional requirements, biochemical properties, and pathogenicity to experimental animals. Immunological studies are not yet complete. Transformation of H. vaginalis into the L form of colony is described and illustrated in a series of photomicrographs. It is suggested that the pleuropneumonia-like organisms frequently encountered in genitourinary infections are, in fact, L forms of H. vaginalis. Attention must in future be concentrated on the normal bacterial phase and not on the L phase which is probably not pathogenic.

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Minimal quantities of active vaccinia virus in the form of a purified elementary body suspension were injected subcutaneously into rabbits. The amount administered was about 10 minimal infective doses as measured by intracutaneous titration and tissue culture assay: this is equivalent to about 1·3± 10−5μg of virus protein. The immune response to this minimal quantity of virus was determined by complement-fixation and virus neutralization tests and also by skin sensitivity tests. The results indicated that viral proliferation occurred to an extent sufficient to sensitize the tissues to the virus protein. Measurable amounts of antibody could also be detected in about one half of the experimental animals. A second inoculation of virus produced a considerable augmentation of the immune response. Viral proliferation must have taken place in order to evoke this immunity, but infection always remained at the subclinical level. The results were much improved when the infecting does of virus was incorporated in an adjuvant. DPT-polio vaccine functioned well as adjuvant but equally good results were obtained with a solution of polyvinylpyrrolidone. The latter substance also has valuable properties as a protective colloid and is thus able to maintain the viability of the virus over long periods of time.On the evidence provided by these experiments it is suggested that an adequate immunity to smallpox might be achieved in man by similar methods. A primary sensitization could be achieved by incorporating a very small amount of active virus in one of the prophylactics given as a routine in the early months of life. This could be followed by normal jennerian vaccination a few months later; or the second inoculation of virus could also be incorporated in amultivalent prophylactic. For adults, a somewhat similar two-stage immunization would be required.It is hoped that the publication of these preliminary experiments will encourage other investigators to continue what promises to be an important line of research.All assays involving the use of monkey kidney tissue cultures were carried out by my former assistant Mr Edmund Bischoff. His help is gratefully acknowledged.

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