DEFINITION OF THE PULSE FLOW
In determining the blood-flow to the arm by a method which we have described,1 the arm is enclosed in a plethysomograph and the venous outflow is obstructed by suddenly raising the pressure in a cuff placed just outside of the instrument. The pressure applied is not sufficiently high to interfere with the free entrance of arterial blood. As a result of this obstruction, the arm begins to swell. The rate of swelling is at first fairly uniform ; but later, as the pressure in the blood-vessels rises, there is a falling off in the rate of swelling due, on the one hand, to an escape of venous blood beneath the pressure cuff, and on the other to the force opposed to the entering arterial stream by the rising pressure in the capillaries and arterioles. For a brief period, however, the