The growth curve of rabbit skin-adapted vaccinia virus in the chick chorioallantoic membrane incubated in Hanks' solution showed a drop in titre of virus for about 10 hr. followed by growth. At least 25% of virus, sometimes more, remained infective. A similar fall in titre was observed in heated membranes in which the virus did not grow and this occurred also when membranes, either normal or heated, were infected and disintegrated before incubation.
The growth curve of virus in minced chick-embryo was similar to that in chorioallantoic membrane.
Virus in cell suspensions prepared from chick embryo and incubated in a nutrient medium showed only a small loss of infectivity before growth in some experiments and rarely dropped below 65–70 % of the original titre in others.
These results throw considerable doubt on the view that loss of infectivity preceding growth of vaccinia virus should be interpreted as an essential part of a growth cycle.
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