Ultrastructure of the Rabbit Papilloma Virus

The ultrastructure of the rabbit papilloma virus particle has been studied by electron micrography of thin sections of the purified agent, obtained from 7 different batches of warts occurring naturally in cottontail rabbits. In preparations treated by procedures including fixation with osmic acid and staining with uranyl acetate and lead hydroxide, there were observed essentially circular images, 26 to 29 mµ diameter, exhibiting a densely stained internal structure. This was distributed in a thick threadlike or granular form and filled most of the demonstrable substance of the particle. There were also numerous images of low contrast resembling “ghost” forms seen in preparations of other filterable agents. The appearance of the images differed greatly from that of other viruses associated with tumors. The results are discussed in relation to the constitution of purified tumor viruses and its bearing on the demonstration of structure with the stains employed.