Rabbits, convalescent from vaccinia and in good general health, were subjected to infection with myxoma during a period of exposure to a high external temperature. It was observed that in proportion as the temperature was elevated, a profound change in the course of the myxoma infection occurred. At the highest temperatures, the disease was held completely in abeyance, and no lesions appeared within 17 days of observation. At lower temperatures, lesions appeared which tended to be circumscribed, and which reached their maximum development within 6 or 8 days after inoculation. Regression then set in and complete healing occurred. There was wide variation in the degree of protection which a given temperature conferred on an individual rabbit as measured by the amount of virus required to cause infection, although for single animals the difference in concentration of virus required to produce consistently positive and consistently negative results was not apparently different from that obtaining in the controls. With the data at hand, it does not appear justifiable to draw final conclusions as to the state of immunity of the animals which survived the modified infection.

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