| 摘要 |
<p>A hog cholera vaccine of reduced virulence is obtained by inoculating another animal, such as a rabbit, in which the hog cholera virus will not ordinarily propagate, with a normal strain of hog cholera virus, preparing an inoculum from said other animal, e.g. from the spleen thereof, after a period of one to six days and injecting a non-immune hog therewith, allowing the virus thus transferred to propagate in the hog, preparing another inoculum from said hog and injecting the viral preparation into a second such other animal, repeating said alternate passages until the virus is so modified that it will propagate in such other animal, continuing serial passages of the modified virus through a plurality of such other animals, removing the virus and preparing a vaccine therefrom. At least five and preferably twenty animal passages are required to produce a satisfactory virus. If desired, one or more alternate passages through a hog may be included in the plurality of serial passages through the other animal. In the example rabbit-hog passages are repeated until the rabbit commences to show signs of fever whereupon the virus is propagated through rabbit passages alone, the inoculum being prepared from rabbits in the febrile condition.</p> |
