Vasomotor and other circulatory disturbances of the extremities have been the subject of a great deal of study and investigation at the Mount Sinai Hospital, Cleveland, on account of both the relatively large numbers of cases coming under observation and the paucity of our medical knowledge concerning them. Up to a few years ago, one of the greatest obstacles to a more extended study was the lack of an accurate and convenient method of measuring the blood supply. A given case may have presented the picture of cold, painful and cyanotic extremities, with the limb changing rapidly from purple to waxy white and back again, on elevation of the limb and then lowering it below the level of the body; and if the pulse in the dorsalis pedis artery was absent, it was held that the patient had a serious obstruction to circulation. If the same conditions were present, except