The technique is described whereby vaccinia "granules" are separated from all other material of glycerolated vaccinia calf lymph and cultivated in vitro with embryonic tissues.

These "granules"remain alive, as tested by rabbit corneal inoculation, for as long as 71 days, when grown in connection with growing tissue; they fail to remain potent if cultivated with dying cells, showing in this way the same characteristics as whole vaccine virus. The potency of the " granules" increases with the age of the culture under the first mentioned conditions.

The fluid part of the vaccinia lymph which remains after the removal of all "granules," is impotent under all conditions.

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