A method has been devised to determine the location of infective Shope virus in the papillomas of cottontail rabbits. Frozen sections of the growths were burned selectively with a microcautery to destroy either the keratinized or proliferating layer and the sections were then applied directly to the sensitized epidermis of domestic rabbits. No papillomas appeared when the keratohyaline and keratinized areas had been eliminated leaving the proliferating cell layer, whereas papillomas arose when the proliferating cell areas were destroyed leaving the keratohyaline and keratinized layers. The results indicate that infective Shope papilloma virus is situated mainly, perhaps entirely, in the keratohyaline and keratinized areas of cottontail papillomas. This is in accord with the previous disclosure by the fluorescence technique that virus antigen in demonstrable quantity is present only in these situations.

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