MICRO-INJECTION STUDIES OF CAPILLARY PERMEABILITY

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Abstract
By a micro-injection method permiting determination of capillary pressures in single capillaries of frog mesentery the possible factors in the production of concentration of corpuscles within the capillary are considered. A rise of capillary pressure to the arteriolar level is accompanied by a slow concentration of corpuscles, but the filtration of fluid is not sufficient to cause complete stasis. Typical concentration of cells and stasis, such as described for dilated capillaries by Krogh, can be produced locally by mechanical injury without change in diameter. The filtration of plasma is influenced by capillary pressure. Direct measurement indicates that dilute urethane causes a rise in capillary pressure of 2-6 cm. water, later followed by a further increase to above 25 cm. as stasis appears in the venous capillaries. Increased permeability to urethane has been observed in constricted and in dilated capillaries without change in diameter. In the strengths required to cause increase of endothelial permeability, urethane kills Paramecium caudatum and developing marine eggs. In view of these findings it appears that the increased passage of fluid observed after application of urethane is not due to dilatation but to injury of the capillary wall, accompanied by increased capillary pressure. These facts are opposed to Krogh''s theory of capillary permeability, which is based largely on the view that the increased permeability after urethane is due solely to dilatation.

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