A new method is described for the quantitative study of leucocyte migration. Blood drawn into a capillary tube is centrifuged, forming a buffy coat. The migration of the leucocytes from the buffy coat into the plasma is measured by means of an ocular micrometer.

While there is a great deal of variation from one normal individual to another in the migration rates of leucocytes those of each individual show relatively little variation in migration from day to day (Table I).

In all cases of illness studied, the average migration rates fall within the normal range, but there was a wider variation in the day to day migration rate than obtains in normal healthy individuals (Tables II and III).

From experiments in which the cells with typically "slow" and "fast" migration rates were tested in both the "slow" and "fast" plasmas, it could be concluded that while the cells invariably have some influence on the migration rate, the major factors influencing leucocyte migration reside in the plasma (Table V).

Experiments in which the plasma proteins were fractionated according to the method of Lever et al. indicated the presence of a system of proteins which regulate leucocyte migration. A heat-labile (56°C. for 30 minutes) component of fraction II was able to accelerate leucocyte migration, while fraction III acted as an inhibitor (Tables IX and X).

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