GENERAL CONSIDERATIONS By methods which have been described elsewhere1we are able to determine (a) the average blood flow in the arm of man over brief periods of time, (b) the volume and form of the pulse wave entering the arm, and (c) the blood flow in the main arm arteries during each portion of the pulse cycle. The last, which we have called the pulse flow in the brachial artery, may be recorded directly. It is, however, a resultant of the two preceding components; that is, of the average blood flow and of the variations in this flow produced by the entrance of the pulse wave into the arm. The average rate of blood flow in the arm depends in part on the average blood pressure, and in part on the local resistance opposed to the flow of blood through the smaller arteries and capillaries of the arm. By