TRANSFORMATION OF THE SHEEP-POX VIRUS INTO THE VACCINIA VIRUS BY MEANS OF TESTICULAR PASSAGE OF RABBITS

I. The passage of the sheep-pox virus made through rabbit's testicles in successive inoculations of a piece of testicular tissues of each generation of which the first one having been inoculated intratesticularily with the skin eruptions, nodules of the lung, blood, lymphatic glands or bone-marrow obtained from an infected sheep may, upon the first or the third generation at the latest, present the typical lesions as the usual cow-pox virus does upon testicles of this animal. These lesions become more and more pronounced as the generations go on.II. The testicular emulsion on the first generation remains always inert by the cutaneous inoculations upon calves, but the same after 2-4 passages at the latest, form the typical vesicles exactly same and indistinguishable from one produced by common cow-pox, which is seen more and more marked as the generations step on, fairly corresponding with the macroscopic changes in testicles.III. The lymph prepared by the usual method from the vesicles produced on a calf with sheep-pox virus, which was passed through rabbit's testicles, may form on the skin of primary vaccinating infants the beautiful vesicles exactly similar to that of usual vaccine lymph.IV. The immunity against common cow-pox virus rendered the rabbits, which were previously used for the sheep-pox passages, is found, about three weeks after the intratesticular inoculations, gradually becoming complete with the progress of generation, although no trace of immunity could be demonstrated in the first generation.V. Powerful common cow-pox lymph effects absolutely inactive on a calf, which was inoculated with sheep-pox virus of 3-4 intratesticular passages in rabbits 16-20 days before, that is to say, the sheep-pox virus after passing through rabbit's testicles, differing from its original virus, maintain a complete immunizing property against cow-pox virus.VI. The sheep-pox virus after intratesticular passages in rabbits considerably decreases its pathogenic character to sheep, as far as if with usual cow-pox virus.VII. Sheep 19-20 days after having been inoculated with sheep-pox virus passed through rabbits intratesticularily are, by intravenous injection of the sheep-pox virus, typically affected with sheep-pox with exactly same incubation period as the untreated control, only remaining alive while the latter died of the disease after a week, and although it may still be beyond the determination as this minor number of the experimental animals would not stand for, that it is due to the fact of the incomplete immunization by the sheep-pox virus passed intratesticularily in rabbits, at least so far may be said with certainty, that the sheep-pox virus, after being passed through rabbit's testicles, renders the animal immune against the common cow-pox virus, losing, at the same time, the majority of its immunizing property against the original sheep-pox virus.VIII. The sheep-pox virus is found transformed, as the above described experiments approve, perfectly into the cow-pox virus by passages through the testicular tissue of ascertaining that the small-pox and sheep-pox virus are, as being believed as such hithero, in very close relationship.