This monograph is the result of the personal hemocytologic studies of the authors, on which much time and care have been expended. Although the conclusions may not be universally accepted, they are deserving of much consideration. The method of staining used by these workers is a combination of the Jenner and Giemsa stains, a method advocated by Pappenheim and one giving extremely panoptic results. Control studies were made with a variety of other staining methods. This work is especially commended to those who are interested in the histology of the blood-cells. It is only through such isolated investigations as these that our knowledge may be rounded into that complete whole which is so necessary before the direct application may be made to the solving of the problems of the pathologic variations in the blood-cells. The style of presentation is clear, concise and convincing. The illustrations are excellent.