Abstract
Syverton and Berry 1 reported the successful cultivation of the virus of St. Louis encephalitis (epidemic encephalitis, Type B) in a medium containing minced living embryonic mouse-brains. Later, Harrison and Moore, 2 confirmed this work and in addition reported success in propagating the virus on the chorioallantoic membranes of developing chicks. This paper is a confirmation of both these reports.
The methods followed in our studies were in all essential respects the same as those reported by our predecessors. The mouse-embryo method was the same as that employed by Syverton and Berry, with the exception that 0.4 cc of material was transferred serially to culture-wells containing 2.5 cc of Tyrode's solution, 0.5 cc of normal rabbit serum and 0.5 cc of finely minced embryonic brains in Tyrode's solution (five, 14-day embryo-brains in 10 cc Tyrode's). Both the Li and Rivers 3 collar-flasks and 1 ounce flat-sided screw-cap bottles were used as receptacles for the medium. In propagating the virus on chorioallantoic membranes we initially followed the procedure (work carried out in 1936) described by Woodruff and Goodpasture, 4 and later a modification of this technic introduced by Burnet. 5 One-tenth cubic centimeter of a 10% suspension of the freshly harvested membrane in Tyrode's was inoculated in making the transfers. Ten- to 14-day eggs were employed. Webster's virus, strain No. 3, was used throughout.
The embryonic mouse-brain cultures of the virus were carried through 16 passages, with a final titer of 10-3. From the 6th passage on, the virus was also carried on 2 additional media: (a) minced adult brain in place of embryonic brain, (b) minced adult brain without serum; the difference in volume was made up with Tyrode's solution. In both cases the virus was carried to the 12th passage (6 passages on adult brain), but in both it disappeared by the 14th passage.
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