of 0.rford BECAUSE disease of arteries is now so common, it becomes more than ever necessary to have as clear an idea as possible of the behaviour of the individual elements of the arterial wall in different circumstances in order to understand the factors involved in the disease process.This paper records observations made on the behavioiir of arterial endothelium of the rabbit after removal of a patch of endothelial cells from the abdominal aorta, EXPERTMENTAL METIIODS OperationUnder nembutal and ether anmthesia and with full asepsis the lower abdominal aorta and its bifurcation were exposed through a midline incision. A small spring clamp with blades covered with rubber was placed on the aorta just below the renal arteries. A thread was tied around the right common iliac artery about 1 cm. from the bifurcation and an untied loop of thread passed around it just distal to the bifurcation. An incision was made in the common iliac artery between the two threads. A brass rod of such a diameter that it just filled the lower abdominal aorta ww then passed into the aorta via the incision in the common iliac artery, rotated gently in contact with the arterial wall up to the level of the origin of the inferior mosenteric artery and withdrawn. The rod was roughened for about 1 cm. behind its conical tip to increase its chances of removing endothelium. As the rod was withdrawn the loose thread on the iliac artery was tied and the clamp removed from the aorta. By this procedure tho intima of the artery was damaged without interfering with the vasa vasorum to that part of the vessel.Some animals were weak in the right hind leg for a few days after operation, but only 2 out of 106 animals showed any sign or impaired circulation in the foot and these were killed a t once.Young rabbits weighing approximately 2 kg. were used. Preparation of materialProbably more information is obtained by observing endothelial cells en. face than from sections cut perpendicularly or obliquely to the surface. As long ago as I884 Zahn examined in rabbits the healing of a small arterial lesion caused by tying a ligature tightly round the vessel and then releasing it, a procedure which tore the intima. After a variable time the animal was killed, the artery dissected out, the adventitia removed and the artery opened and pinned out on pith. The " borders " of the endothelial cclls were stained with silver nitrate.A similar though improved technique has been exploited by Lautsch, McMillan and Duff (1953) who modified the method of O'Neill (1947) for the * Locke Research Fellow of' the Royal Society.

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When the sodium salts of certain fatty acids were added to rat blood in vitro, the production of artificial thrombi by a modification of Chandler's method was significantly altered: thrombus‐formation time was accelerated greatly and longer thrombi were produced. Straight‐chain, saturated fatty acids with sixteen to twenty‐six carbon atoms were strongly active. Short‐chain fatty acids, C 6 and C 7, were inactive. The four long‐chain, unsaturated fatty acids tested, oleic, elaidic, ricinoleic, and arachidonic, were inactive or very nearly so. The activity of a long‐chain fatty acid such as stearate, was reduced by the addition of methyl groups.