Since Askanazy'sinitial studies on reticulated red cells, others (Keyes,' Cunningham, Seyfarth, Pappenheim, Isaacs, and Ferrata) have contributed findings which have somewhat clarified the significance, properties and characteristics of reticulocytes in the peripheral blood stream. The result is today's widely accepted concept that young erythrocytes manifest themselves on the stained slide as polychromatophilic, stippled, or reticulated forms depending on the amount, distribution, and state of the basophilic reticulum within the cell. The duration of contact between the stain and the basophilic material is important for the demonstration of these immature cells, as is seen by the invariably higher reticulocyte counts which are secured when a wet method of staining them is used (the blood being held in longer contact with the stain as a solution), as compared with dry methods. This doubtless accounts for the varying normal values of reticulocytes (0 to 4.0 per cent) in the literature. The nature of the basophilic reticulum in the red cell which may assume a polychromatophilic, stippled, or reticulated appearance is not proven. It occurs in the normal process of maturation of the erythrocyte. Three origins have been suggested. One proposed by Naegeli and Seyfarth considers the material a product of nuclear decomposition. Keys and Dawson recently considered a genetic relation of the reticulum network to mitochrondia. The most widely accepted concept today considers the basophilic reticulum as retained undifferentiated cytoplasmic