METHODS Male albino Wistar rats weighing 280-320 g were anaesthetized with ether. The abdomen was opened and thepancreatico-duodenal, ileo-colic and colic branches of the superior mesenteric artery were tied. The superior mesenteric artery was separated from surrounding tissues in the region of the aorta and a glass cannula was inserted distally into the artery at its origin from the aorta. While the artery was being prepared for cannulation the connexions of the superior mesenteric plexus to the coeliac ganglia were severed. The rat was killed (under ether) by opening the thorax, and the intestine was separated from the mesentery by cutting close to the intestinal border of the mesentery. The perfusion apparatus was essentially similar to that described by Fastier & Smirk (1947) for the perfusion of isolated rat hind quarters. Ringer-Locke's solution was oxygenated with 95% 02 and 5% CO2 and was delivered at a constant rate (2 ml./min) by a roller pump to a heat-exchange coil immersed in a constant temperature bath at 370 C and thence to the cannula inserted into the superior mesenteric artery. The perfusion pressure was measuredmanometrically.

During the perfusion the isolated mesentery lay on a stand just above the constanttemperature bath and was covered with cotton wool moistened with warmed Ringer-Locke's solution. By adjustment of infra-red lamps above the bath the temperature of the preparation was maintained at 370 C. Most of the perfusate flowed out from the cut ends of the vessels on the intestinal margin of the mesentery but some flowed out from the cut end 2 Physiol. 177