Clinical studies of capillary circulation received a marked impetus when Lombard,1in 1912, elaborated his method of direct visual examination of the capillaries of the skin. The capillary system is probably the most important unit of the entire circulatory apparatus, and yet, to quote Krogh,2"it is a little strange that... the capillaries have been neglected in an extraordinary degree." Since microscopy of the capillaries has permitted a study of their morphology, distribution and behavior in health and disease, a new field has been opened to physiologists as well as to clinicians. The function of the circulatory system is twofold; viz., to carry nourishment to the tissues and to carry waste products away from the tissues. The capillaries are all-important since it is through their walls that this exchange of food and excretion products takes place. It must be apparent, therefore, that many pathologic conditions will be better