Chronic secondary anemia may be divided into three general groups: a type due to hemorrhage, a type due to some organic lesion, and, after all known causes of anemia have been excluded, a type which it has been necessary to classify as idiopathic secondary anemia. The last-named type has been difficult to treat in comparison with the first two types, which respond as a rule following removal of the causative factor. Because of difficulty in the treatment of the forms of idiopathic secondary anemia, it seemed that a study of the morphology of the blood in these cases might throw some light on the condition of the hematopoietic organs, and thus might enable treatment to be directed toward restoring normal hematopoietic function. Before discussing the morphologic blood picture in idiopathic secondary anemia, it is well to list the more characteristic features of regeneration and degeneration of the blood that appear