Intravenous injection into rabbits of bacterial endotoxins results in an inhibition of migration of leucocytes from the buffy coat of their blood in tissue culture or in "slide cell" preparations. This effect was demonstrable 5 minutes after the intravenous injection and persisted for from 6 to 12 hours after the injection. It is as marked in rabbits receiving only a single intravenous injection of endotoxin as in those previously prepared intradermally and developing a severe local Shwartzman reaction on intravenous injection. The preparation of the skin for the Shwartzman reaction does not in itself result in appreciable changes of leucocyte migration. The production of the effect depends upon some action in vivo, since leucocytes of uninjected rabbits migrate normally from the buffy coat in plasma substrates to which large concentrations of endotoxin are added in vitro. The inhibitory effect, as observed in these experiments, also depends upon the added influence of centrifugation. Leucocytes from a rabbit receiving endotoxin intravenously migrate normally from uncentrifuged lung or spleen fragments and migrate normally in blood on the warm stage prior to centrifugation. Identical centrifugation does not affect leucocytes from uninjected animals. The heparin inhibition of the local Shwartzman reaction does not alter this effect of endotoxins on leucocytes. Its possible role in the production of leucopenia and of the local Shwartzman reaction is briefly discussed.

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