THIS study was undertaken becaucse, in the course of another series of investigations, we became aware of the possibilities that one of the more recently developed plastics, polythene (polyethylene), might have in clinical surgery. Since we had been impressed with the physical characteristics of polythene and with its evident tolerance by one of the most sensitive of tissues, the intima of lymphatic vessels and veins, it was not long before we wished to determine what uses it might have to supplant, in part, living tissues and structures. We were aware of the history of the uses of foreign materials in living tissues. On the one hand, ligatures and sutures of certain materials have been proved by centuries of use to be tolerated by living tissues; in fact, before the introduction of the ligature, surgery consisted only in the treatment of suppuration. On the other hand, almost every proposed use of a foreign material to replace or fill a