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~~~~~~~~~~~ to-sideto the aorta, in which an-------< oval window had been cut to make FIG. 4.-Microscopical section (x 55) of the aortic stoma orion and collagen four months after in-larger These endsertion. Spaces near the orlon arearte-to-side and side-facts. The thickness of collagen is to-side anastogreater on the exterior (see text). moses were tried because they made possible a larger stoma than would end-to-end anastomosis, in which the stoma would, of course, be limited to a diameter equal to that of the host artery. A large stoma, and particularly one in which the suture line did not completely encircle the host vessel, should be less liable to closure by thrombosis. The end-to-side and side-to-side anastomoses worked well in the aortas of dogs in which they were tried. The posterior peritoneum was closed over the prosthesis and the abdomen closed in layers. Penicillin and" plas-mosan" were givenpost-operatively. At a later date patency of the grafts was determined by an aortogram per-formed by injecting diodone into the aorta above the pros-thesis through a cardiac catheter which had been passed down into the aorta from the common carotid artery (Fig. 2). The results in the dogs which had orlon prostheses are shown in the Table. The prostheses were implanted in their abdominal aortas or as shunts around an aortic or iliac obstruction. One (G. 10) died 10 hours after operation without recovering from the anaesthetic. The prosthesis was patent and lined internally by smooth fibrin. The anasto-mosis was intact. Another (G. 3) died at 16 weeks post-operatively from rupture ofa false aneurysm that was surrounding the prosthesis and which had formed from an anastomotic leak. The orlon tube was floating in the centre of the false aneurysmal sac and had no fibrous reaction within or around it. The significance of this lack of reaction is discussed below. The suture material was found to have pulled out of the aorta at the distal anastomosis. In one animal (G. 11) a 5-in.(12.5-cm.) long shunt had been placed from the aorta to the left common iliac artery, bridging a tape ligature on the iliac artery. The shunt thrombosed in the early post-operative period, and on sacrifice at four weeks the graft was found to be thrombosed and one of the distal anastomotic sutures had constricted the iliac artery. All the other orlon prostheses have remained patent. The two failures were due to technical errors which were in no way peculiar to the material or the method.

The tubes become lined with a smooth glistening layer of hyaline collagenous tissue, the innermost layer indistinguish-able from intima (Figs. 3 and 4). They are surrounded by a thick layer of fibrous tissue which encases and grows into the meshes of the cloth (Fig. 5). They are tolerated without ill effect. The collagen lining and surrounding the tube results from the vascularity and activity of the surrounding tissues. This was well shown in dog G. 3. Rupture of the distal suture line occurred soon after operation, and blood continued to flow through and around the tubeand into the false aneurysmal sac, in which it lay almost free for several months before death. Despite this, the orlon tubelooked almost as fresh as when it was inserted. There was a little fibrin deposited on it, but no collagen formation whatever. This suggests that contact with surrounding living tissues may be necessary for the collagen to form. Mere contact with circulating blood is insufficient. Another interesting point that emerged at necropsy was the way in which the orlon retained its strength. After several months in the tissues the tensile strength of the fabric appeared to be quite unchanged. This is of great practical importance, because mere …