Consecutive weekly observations on the total white cell count of the peripheral blood were made on 5 groups of normal rabbits, a total of 45 animals, during a period of 20 months from October, 1927 to July, 1929. The duration of individual group examinations varied from 8 to 35 weeks.

In the case of 4 groups followed 13 to 35 weeks, the general trend of the total white cell means was toward increasing values; with the group followed 8 weeks, the means were maintained at a constant level.

The changes in the levels of the granular cell means were usually accompanied by changes in a similar direction of the non-granular cell means. In the case of 3 of the 4 groups followed for the longest periods, the greatest relative alterations occurred in the non-granular cells.

The fluctuations in the mean values of the total white cells and of the granular and the non-granular cells which were observed in one group of rabbits, were also generally observed in another group examined during the same months.

The period of greatest irregularity in the mean values of the total white cell means and of the granular and the non-granular cell means as well, occurred during the late winter and spring months of both years.

The general level of the total white cell mean values in the groups examined during 1927–28 was higher than that of the groups observed during 1928–29. A similar difference was found in the granular and non-granular mean values but it was somewhat less marked in the case of the granular cells.

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