Vaccination with vaccine virus of a rabbit colony of approximately 1500 animals was carried out as a prophylactic measure against rabbit pox. The observations made on the adult population are discussed in the present paper.Of 233 presumably susceptible animals, 195 or 83.7 per cent gave a positive local reaction to vaccination. Generalized lesions, comprising in particular cutaneous and mucocutaneous papules, adenopathy, and in males an orchitis, developed in 78 animals, an incidence of 33.5 per cent. Nine of these cases had had a negative vaccination. Clinical evidence of susceptibility to vaccinal infection was thus demonstrated in 204 presumably susceptible rabbits, an incidence of 87.6 per cent.Of 310 rabbits which had recovered from rabbit pox ten months previously and were, therefore, presumably refractory to vaccination with vaccine virus, 294 or 92.3 per cent gave completely negative results. A positive reaction to vaccination developed in 21 animals, however, and there were 3 cases of generalized lesions in animals with a negative local vaccination site, a result which shows that the refractory state induced by rabbit pox may eventually disappear.An outstanding feature of the results concerned the different character of the reaction of female as compared with male rabbits. A slight, even a negative, local reaction to vaccination was often observed in females and there were comparatively few cases of generalized lesions. This type of reaction was especially striking in the case of pregnant animals. The differences between the lower incidence of both local and generalized lesions in pregnant rabbits as compared with males were found to be statistically significant.
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