Within the past few years, chiefly because of better knowledge of the physiology of the blood, much new light has been thrown on a group of diseases which have always aroused great interest, but whose pathology has been obscure, and whose treatment has been exceedingly unsatisfactory.
Of these diseases, the most important clinical feature of which is a tendency to uncontrollable hemorrhage, the most important to pediatrics are the so-called melena neonatorum, the purpuras and hemophilia; the last being, of course, equally evident in later life. Etiologically, we are still in the dark regarding all of them. Hemophilia shows two very important differences from the others. It is a permanent, not a temporary condition, and it is not characterized by spontaneous bleeding or oozing from the vessels, but merely by failure of the ordinary method by which a break in the vessel wall is sealed after it occurs. In purpura,