In the course of experiments performed on rats to produce hypertension by wrapping regenerated cellulose film (cellophane) around one kidney, the accidental observation was made that several rats developed sarcomas in the neighborhood of the cellophane. As it was known that spontaneous sarcomas are a rarity in this Sherman strain of albino rats it was decided to investigate this question as an independent problem.Method. The cellophane employed was regenerated cellulose film, the particular sample used throughout these experiments being known as Visking 5-% H.S. ("highstretch") cellulose sausage casing. Two strains of albino rats were used, the Sherman and the Wistar. The rats were fed on a mixture of Purina Laboratory Chow and Rockland Rat Diet in pellet form.Cellophane was introduced by two methods into 110 male rats, 8 to 10 months old. In 55 of these, the left kidney was loosely wrapped with cellophane according tu the familiar methodl introduced by Page.lr2 In the other 55 rats, a piece of cellophane 2-3 cm square was embedded subcutaneously in the abdominal wall, with a catgut suture passed through the corners to keep the film flat. At frequent intervals the site of the cellophane was palpated by an experienced technician to ascertain if any growth had started. The tumors were usually allowed to grow to a large size (2-5.5 cm in diameter) before the rats were sacrificed for histological examination, Wherever possible, transplants were made from each tumor into 8-16 rats, usually males (but in some instances females), 6-8 months of age. A total of 422 rats were used for this IPage, I. H., Science, 1939, 89, 273. 2 Graef, I., and Page, I. H., Am. J . Path., 1940, ----16, 211.purpose, transplantation (being carried out in some instances to the third, fourth and even fifth generation. Transplants were made by inoculating fragments of tumor tissue (0.003 to 0.006 g) subcutaneously into the anterior abdominal wall by means of a hollow platinum-iridium needle.Results. As in the original accidental observation, a number of tumors were induced at the site of insertion of the cellophane. More than 1 1 months were required for their development. In the perirenal series the shortest time taken for the production of a tumor was 362 days from the date of wrapping to the development of a tumor 8 mm in diameter, whereas in the subcutaneous series the shortest period for development was 471 days.Consequently, those rats that died from other causes within 11 months from the date of cellophane insertion were excluded alltogether from the statistics, since they did not live long enough to develop induced tumors.Among the rats with wrapped kidneys only 23 survived over 11 months, and of these 8 (34.8%) developed large well-defined tumors. Of the 55 rats in which the cellophane was embedded subcutaneously 42 survived beyand 11 months, and of these 15 (35.7%) presented tumors. The diagnosis of all these tumors was confirmed by microscopic examination.The tumors resulting from transplantation appeared after 7 to 175 days. A total ...