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These studies were begun and part of them were made in the laboratory and under the inspiration of my beloved teacher and master, the late Profeemr Franklin 1' . 1Clal17 and it is with a sense of the deepest gratitude and reverence that I acknowledge the immeasurable debt which I owe to him. IKTRODUCTION

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INTRODUOTIONThe growth of new blood vessels in the living mammal, as observed in transparent chambers installed in the ears of rabbits, has been studied microscopically and described in detail ( Sandison, '28 ; Clark et al., '31 ; Clark and Clark, '39).Briefly, it was found that new capillaries arose as endothelial outgrowths from preexisting vascular endothelium, which advanced as blindly ending sprouts, anastomosed with neighboring sprouts to form loops and continued to advance as a plexus with a growing edge of new sprouts. Although the pattern of the new vascular network in each chamber, like that of the intact ear, was different, in standard round table chambers of uniform size and controlled thickness, the tempo at which new capillaries entered the observation space (average of 7 days after the operation) and the rate at which they advanced across it (0.2 to 0.65 mm. per diem) were relatively uniform.The primitive form of the growing vascular network was at first that of an indifferent capillary plexus but as it continued to advance the older portions of the plexus near the table edge soon showed differentiation of vessels receiving a greater supply and drainage into arterioles and venules. Simultaneously, many of the intervening capillaries retracted and disappeared. Vascularization of the table space was usually complete at 2 to 3 weeks after the operation when the sprouts from opposite sides of the table met and anastomosed.