When large amounts of brilliant vital red are injected into the blood stream of dogs, the dye is gradually removed from circulation, and most of it is deposited in numerous phagocytic cells which are scattered throughout various organs and tissues. The dye occurs largely in the form of tiny red granules crowded together in the cytoplasm of these cells.

If Niagara sky blue, a closely related dyestuff, is injected, it too is taken up and stored in these same cells. It is shown that the presence of red dye in the tissues does not inhibit the cells from taking up the blue one.

The normal ability of the phagocytes to take up Niagara sky blue is observed also when this dye is injected simultaneously with brilliant vital red. This normal response toward the blue dye is seen even though the phagocytes are busied at the same time in the process of engulfing and storing the red dye.

These experiments show that it is difficult if not impossible to "block" the cells with one dye so that their ability to take up another is even slightly impaired.

The two dyes employed in these studies are shown to be particularly suitable for experiments of the sort here reported.

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