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Reminiscences of work on capillary circulation

, : Reminiscences of work on capillary circulation. Isis 41(1): 14-20

This is an informal lecture to Harvard medical students, 1946, by Prof. Krogh on the background for, and the history of his Nobel Price winning (1920) work on capillary circulation. While a student in zoology he became interested in physiology. Upon graduation in 1899 he was assistant to Prof. Christian Bohr, who believed oxygen to be "secreted" by the epithelium of the lungs into the blood. Seeking decisive evidence for this theory, Dr. and Mrs. Krogh became convinced that the passage was by simple diffusion. Made lecturer in the University and given a small laboratory in 1910, Krogh and I. Lindhard studied muscle work and developed a method of determining the cardiac output in man by means of nitrous oxide. This showed an enormous increase in circulation rate induced by muscular work, and it became clear that the increase in oxygen consumption takes place mainly in working muscles. While speculating on the function of the mechanism, he saw that, if the supply was just right during rest, no increase in the rate of flow through the same capillaries would make it sufficient for the 10-fold increase in oxygen consumption during work. Then it occurred to him that the anatomical arrangement of parallel muscle fibers and capillaries would work beautifully if during rest only a small fraction of the capillaries are open to the passage of blood, and during work a local lack of oxygen would cause the nearest closed capillary to open. To test this idea 2 instruments were devised and used to measure the diffusion of oxygen through muscular tissue, and microscopical observations were made in vivo on thin muscles of frog and guinea pig during rest and when tetanized. Tables of results support the contention that the distance between open capillaries is closely related to the metabolic requirements.


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