Abstract
Summary
After 68 passages on the chorio-allantoic membrane of the chick there is no increased proliferation of the virus on the membrane. The virulence of this virus after cultivation in eggs for 9 months has been demonstrated to be the same for the mouse as that of the original inoculum of the eggs. The virus content of the chick embryo brain is consistently slightly greater than that of the corresponding chorio-allantoic membrane. The majority of the chicks live until the time of hatching and show no gross changes attributable to the virus and only slight and inconstant microscopical changes in the brain. The membranes show a gross edema and fine granulation of the surface. Microscopically, they show chiefly edema and cellular infiltration of the mesoderm and foci of ectodermal proliferation with superimposed necrosis of the superficial layers.
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