Fluorescein angiography was carried out by modification of method as described by Feindel et al. The hemisphere was widely exposed to allow visualization of surface blood vessels. In the experimental room, the dye was injected rapidly either through a fine polyethylen catheter placed in the lingual artery or thorough the cannula in the femoral vein. For "lingual" angiography 1.6 ml of 1% sodium fluorescein were used, while for "femoral" angiography, 4 ml of 10% solution were injected. In the operating room 4 ml of 1% sodium fluorescein are rapidly injected into an internal carotid catheter. Serial photographs of the passage of the dye through the surface vessels of the hemisphere were taken with a motor-drive Nikon camera at interval of 0.4 seconds, or longer when indicated, starting at the time of the injection. The shutter was synchronized with the discharge of a rapid re-charging stroboscopic light. A wratten gelatin filter 47A (Kodak) was used over the light and a Nikon filter Y52 over the camera lens for Kodak high speed ektachrome film to obtain color photographs. The timing of the interval between photographs was measured to within in 0.4 seconds by recording from a ink written oscillography synchronized with the shutter. Thus the velocity of flow in individual vessels could be calculated from the serial photographs.