In his review of the evidence of functional activity of the capillaries and venules, Hooker3 pointed out that although studies of capillary contractility extend back for a period of fifty years, almost to the time of the discovery of vasomotor nerves, and although the profound significance of the blood stream in the capillary areas for tissue nutrition was recognized at an even earlier period, capillary function is given scant, if any, consideration in discussion of vascular reactions today. The simple hypothesis of vascular control by means of functional activity on the part of the arterioles has been adequate to explain experimental results. Yet, Hooker adds, in recent years a considerable amount of evidence has been collected which goes to show that this conception is inadequate.
An important factor in the revision of our ideas regarding capillary function has been the development of helpful methods of study. Foremost has been