A method has been devised for serological tests with a virus producing rabbit papillomas that become carcinomatous. The discrete character of the growths caused by the virus when suitably diluted fits it notably for quantitative experimentation. It shows no tendency to lie latent in domestic rabbits though it does so on occasion in cottontails, the natural hosts. Sera which partially neutralize it do not alter its character, or attenuate it, but merely cut down the number of its effective entities.

The serum of normal domestic rabbits is ordinarily devoid of neutralizing influence on the virus, but that of animals carrying the papillomas usually exhibits neutralizing power soon after these appear. The rate at which this power increases depends in general upon the amount of papillomatous tissue developing, but exceptions to the rule occur, the presence of fairly large growths being compatible with a lack of such powers in demonstrable amount. Even when the antiviral power is great it has no evident influence on the course of established papillomas, other factors determining whether these enlarge or retrogress. It acts to prevent successful reinoculation of the animal, however.

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