1. Methods are described which make possible the calculation of the number and distribution of the hemic cells of the body.
2. The numbers of these cells in the various blood-forming organs, in the blood outside these areas, and in the total body are summarized in table 3, together with the ratios of the number in the blood to the number outside the hematopoietic organs for the standard 70 Kg. human male. Dividing these figures by 70 will give the values per Kg.
3. By similar methods the values for other age and sex groups in man and for other species may be calculated.
4. Leukocytes apparently are not primarily blood cells but are merely en route in the blood to the defense of body tissue generally. Only 1/40 to 1/400 of the total leukocytes outside the hematopoietic organs are present in the blood stream at any one time.
5. These somewhat surprising figures account for many previously made observations which were hitherto hard to explain.