Further Observations on the Cultivation of Vaccine Virus in Lifeless Media

We have made ten attempts to cultivate vaccine virus in tissue extracts prepared according to the method described by Eagles and Kordi (4). Renal, testicular, and chick embryo extracts were employed with a dermal strain of vaccine virus and with the Levaditi strain of neuro-vaccine virus. In no instance were we able to show that the virus multiplied in the extract media. Both of these strains of virus, however, multiplied in media containing bits of minced viable tissue. Furthermore, treatment of rabbit testicular tissue and chick embryo tissue in the manner described by Eagles and Kordi for the preparation of the extracts leaves some cells not only alive but capable of proliferation. Although the results of our work are not in accord with those obtained by Eagles and Kordi, we offer no explanation for the discrepancy. Nevertheless, one cannot examine the results of our work recorded in the six tables without recognizing the fact that in the types of media used the presence of viable cells appears to be essential for the multiplication of vaccine virus. Rabbit testicular tissue and bits of chick embryos support the regeneration of the active agent more efficiently than does rabbit renal tissue.