Dimensions of blood vessels from distributing artery to collecting vein.

• In a recent study, measurements of lengths, diameters, and numbers of vessels contained in a peripheral vascular bed from distributing artery to arterial capillaries were made in the living animal. From the data, total crosssectional areas of the various portions of the arterial tree were calculated and compared with values from similar measurements of vessels in fixed tissue. In the living animal, a linear increment in total cross-sectional area was found from artery to arterial capillary, differing markedly from the long accepted concept of small increases in total area from artery to arteriole followed by a tremendous increase in area at the level of the capillaries. It was suggested at that time that the wide variance in results of the two studies was due mainly to inaccurate estimates in fixed tissue of the numbers of the various types of vessels, especially the capillaries. Further consideration reveals that vessel diameters may be a more important factor in accounting for the variance.