METHODS Observations of four kinds have been made. The effect of sympathomimetic amines has been examined (1) on the blood pressure, the spleen and the nictitating membrane of the spinal cat;(2) on the arterial resistance and venous outflow of the perfused dog hind leg;(3) on the outflow of the perfused rabbit ear; and (4) on spiral strips of rabbit aorta set up in an isolated organ bath. Spinal cats were prepared under ether anaesthesia, dividing the cord at the 2nd cervical verte-bra and destroying the brain. Records of the spleen volume and of the contractions of the nicti-tating membrane were made as described by Burn (1952). For the hind leg perfusion one dog was bled under ether anaesthesia from the carotid artery intoa jar containing heparin, and its lungs were prepared for perfusion by one of a pair of Dale-Schuster (1928) pumps. Perfusion was begun through the lungs, which were ventilated by oxygen with 5% CO2. A seconddog was then anaes-thetized. After dividing the rectum and the inferior mesenteric artery between ligatures, the right external iliac artery was tied, and a cannula was inserted pointing towards the aorta. The body wall was divided in sections between ligatures along the course ofthe left external iliac artery. Poupart's ligament was cut. Branches of the left external iliac from the aorta to about 1 cm below Poupart's ligament were tied, as were also the corresponding veins. The continuation of the aorta below the origin of the external iliac arteries was tied. When the dissection was complete, perfusion was begun by the second pump through the left hind leg at the moment of tying the aorta to arrest the natural circulation.

In some experiments the left lumbar sympathetic chain was prepared for stimulation; in these the dog was first eviscerated and the left kidneyremoved. After the arrest of the natural circulation, the dog was cut in half, the perfusing cannula was tied into the aorta and the blood collected from the vena cava. By this method the ganglia of the sympathetic chain were perfused. In these experiments there was an interval of 7 min between the arrest of the natural circulation and the start of the perfusion. In all perfusions mass ligatures were tied so as to enclose the whole circumference of the body wall above the area perfused. An outflow record was obtained by using Stephenson's recorder (1949). When stimulating the sympathetic chain shielded electrodes, each a silver plate 3 mm wide, were used; stimuli were square-wave pulses of 2-5 mA strength, 1 msec duration and 20-25/sec frequency.