1. A method is described which permits absolute, area-related bone marrow counts for the total nucleated cells and differential count. The technic is easy, the accuracy satisfactory.

2. Normal values for the marrow of young adults (18-45 years) are given.

3. The method permits comparison of any marrow cells independent from changes of the total cellularity, and it makes serial comparative marrow studies in diseases useful, especially in cases where the cellularity is greatly altered (aplasia, leukemia) and percentage-differential counts are almost impossible to judge properly.

4. Experiments in animals may be followed by absolute marrow counts, without alteration of the cells such as occurs in pipet- and shaking-methods. Experiments with ionizing radiation5 showed clearly the practical value of this technic.

5. A survey is given on some total cell counts in disease, showing the range of pathologic changes to be determined with the technic described. The range is from about 80,000 (in marrow atrophy) to 1.5 million (in small-cell leukemia).

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