The concentration of the transmitting agent of leucosis in fowls, as determined by titration, is approximately the same in the suspensions of blood cells and in cell-free plasma; the smallest amount of plasma producing leucosis was 0.000001 cc. and of cell suspension 0.00001 cc. This observation excludes the possibility that transmission of leucosis by plasma is due to the presence of a small number of leucemic cells in the plasma.

The success of inoculations with plasma (20 to 28 per cent of fowls) is, within wide limits, independent of the amount injected (10–1 to 10–6 cc.). The percentage of successful inoculations with varying quantities of plasma is lower than with corresponding amounts of suspensions of cells (33 to 71 per cent).

When plasma containing the transmitting agent is injected in decreasing amounts the incubation period of the leucosis is conspicuously lengthened. With decreasing amounts of a suspension of leucemic cells the incubation period is not so frequently nor so greatly prolonged.

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