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IN a previous communication a description was given of the lesions that occurred in rabbits when the same area of skin was inoculated by scarification with a suspension of glycerolated Shope papillomas from a cottontail rabbit and a suspension of sheep dermatitis lesions (Selbie, 1946). It was observed that the two infections had a suppressing or interfering effect on each other, and that the magnitude of this effect depended on the timing of the inoculation of the two infective suspensions. The most important results of these experiments, however, were obtained from infectivity tests on the skin of normal rabbits with extracts of papillomas arising from the mixed infection. Papillomas that had arisen from skin inoculated with the two infective suspensions at different times failed to infect rabbits, and in this respect behaved in a manner to be expected of Shope papillomas in the domestic rabbit which are rarely infective. On the other hand, papillomas derived from simultaneous inoculation of both infections proved infective, and the yield of papillomas was greater than that obtained in our hands on the rare occasions that domestic rabbit papillomas had been transmitted.In the present communication it will be shown that the papillomatous infection has been transmitted in domestic rabbits to the 10th serial passage, and that the behaviour of this infection is similar to that found in domestic rabbits that have been inoculated with virus derived from papillomas in cottontail rabbits. MATERIAL AND METHODS.The methods used were essentially the same as those used previously (Selbie, 1946). Market rabbits from various dealers were prepared for inoculation or treatment with croton oil by plucking the fur from one or two areas of skin on both flanks, each area measuring 6 by 8 cm. Passage of the papillomatous infection was carried out by rubbing 4 drops of a 10 per cent saline extract of papillomas from the previous passage into each of the epilated areas of skin after scarification with a needle. Papillomas used for passage, 1 to 20 in number, were removed by operation at the times indicated in Table I, except in the case of Rabbit 2, Passage 8, which was sacrificed. Extracts were prepared and inoculated immediately after removal of the papillomas except for Passage 8, in which case the extract was prepared from papillomas that had been stored at refrigerator temperature for 89 days in 50 per cent glycerol.Two methods were used to alter the receptivity of the skin to the papillomatous infection. The first procedure was to treat the skin before inoculation with six applications of 0-3 per cent of croton oil in acetone on alternate days. In the second procedure the skin was inoculated with a mixed virus suspension

Summary: The effect of acidity on the growth of Cl. botulinum was studied by following changes in the viable count of cultures in acid buffered broths containing bread crumbs, after inoculation with about 104 vegetative cells or spores/ml. In 9 out of 10 experiments growth did not occur below pH 5.0; in the tenth it took place at pH 4.8. There was no significant difference between vegetative cells and spores.

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