The Permea4bility of Blood Capillary Sprouts and Newly Formed Blood Capilla4ries as Compa4red to That of Older Blood Capillar,ies

The literature dealing with the permeability of blood capillaries is voluminous. Nothing appears to have been published, however, concerning the permeability of blood capillary sprouts and newly formed blood capillaries as compared to that of older capillaries. Yet this would seem to be a matter of some importance, since there now appears to be a general agreement (1) that the growth of the entire vascular system, after a brief period of primary differentiation, is accomplished by the sending out of capillary sprouts from pre-existing endothelium, and their anastomosis to form new blood capillaries. Not only are large numbers of blood capillary sprouts and new blood capillaries formed during growth, but also during the repair of wounds. If blood capillary all stages of sprouts and this the newly formed blood capillaries are more permeable than older capillaries, would suggest that there may be a freer exchange of materials between vascular system and the surrounding tissue in all conditions in which sprouts and newly formed capillaries are present in large numbers, such as during growth and during the earlier stages of wound healing. MATERIAL AND METHODS. In the present experiments the permeability of blood capillary sprouts and newly formed blood capillaries, as compared to that of older capillaries, was studied by injecting the blue dye T. 1824l intravenously into rabbits having transparent moat chambers in their ears, and determining the time elapsing between injection of the dye and its appearance in the tissue outside of the sprouts and newly formed capillaries, and the older capillaries. The moat chambers (2) used in these experiments are made of glass and mica, and each encloses a shallow space called the “bay.” Following insertion of the chambers, vascularized tissue grows from the subcutaneous tissue of the ear into the bay through two enkance holes at one end. The bay has a glass bottom and a mica top and is only approximately i5 microns deep. Consequently the blood capillary sprouts, newly formed blood capillaries, and older capillaries in it can be seen distinctly with the microscope.