The present intense interest in substances thought to have a stimulating influence on blood-forming tissues again emphasizes the need for a clearly defined set of criteria by which to judge regeneration.
The picture of a true regeneration is best seen following hemorrhage in the healthy animal. Table 1 gives the data on two experiments in
which the blood count in the rabbit was reduced by hemorrhage. The experiments extend over the recovery period; leukocyte and reticulocyte counts are given. The two points to be especially noted are that rise in red count due to regeneration is slow, and that histologic evidence of regeneration, as indicated by the rise in reticulocytes, is unmistakable. Stained smears show an increase in the number of polychromatophilic cells, and when regeneration is active nucleated reds may appear.
As a contrast to this picture of true regeneration, with the slowly rising count accompanied by an increase