It has been shown that a decrease in HI is demonstrable when all or nearly all cells of the allantois are involved in the infectious process. Once this condition is fulfilled, viral multiplication in the CAM is associated with stepwise breakdown and partial restoration of HI. The periodicity of these steps is in close agreement with earlier reports by others on the duration of primary and secondary cycles of viral multiplication. Periodicity of viral multiplication and of HI breakdown with subsequent restoration is particularly pronounced in eggs pretreated with metaperiodate or with mixtures of periodate and glucose or glycerol.

The stepwise nature of the HI breakdown indicates that it is in some way related to intracellular phases of viral reproduction, and that individual cells produce virus in cycles rather than continuously. A possible mechanism of this process is proposed.