Hemorrhagic diatheses in childhood constitute a variety of disorders with a common tendency to bleed. They may be manifested in the form of petechial spots, purpuric extravasations or ordinary loss of blood from free surfaces. These clinical expressions of a disorder of the blood represent active hemorrhagic disease in all grades of severity. But there is a comparable group of disturbances of the blood in which a tendency to bleed or clot representing potential hemorrhagic disease may be precipitated by a sudden change in the vascular system. These latent aspects of hemorrhagic disease have thus far been neglected.
Hemorrhagic disease, latent or active, results from an alteration in either the vascular system or its blood content. An understanding of the mechanism must be based first on knowledge of the normal formative tissue. The reticulo-endothelium is the common hematopoietic tissue which is capable of giving rise to different varieties of blood