Abstract
SUMMARY: A description is given of techniques used for studying influenza virus infection of the allantoic and chorionic surfaces of the chick chorio-allantoic membrane. It was possible to infect one surface of the membrane at a time and to show that the two layers behaved independently and reacted differently. In contrast to the allantoic layer, the chorionic cells appeared to support only a single cycle of multiplication. This conclusion is based particularly on the small rise of infectivity which occurs following chorionic inoculation of virus, and on the proportion between the amount of virus inoculated and the yield of soluble antigen. Some evidence is presented which suggests that the elementary bodies are less readily released from chorionic cells than from the allantoic cells.