A Comparative Study of the Effects of Imbedding Cellophane and Polystyrene Films in Rats.

The results of imbedding cellophane subcutaneously in rats were compared with previous results with polystyrene; 280 films were imbedded subcutaneously in 140 rats, which were divided into three groups and observed for tumor incidence. All animals were permitted to live out their life span. Group I: Films were removed at monthly intervals from the enveloping pockets induced. Group II : Pockets as well as films were similarly removed and the pockets examined histologically. Group III: Controls; films and pockets in situ throughout. As with polystyrene, no tumors were produced when pockets were excised, and there was a reduction in number when films alone were removed. With polystyrene, film removal before 6 months entirely precluded tumor formation, but with cellophane after film removal, even at 3 months, some tumors still appeared. The control group showed the usual tumor incidence. Histological studies showed a much greater fibroblastic activity with cellophane than with polystyrene, especially in the early months. This may be related to the shorter time of contact necessary to initiate neoplastic change (3 months instead of 6). Other differences found with cellophane are discussed, such as its marked tendency toward calcium deposition in pockets, in tumors, and on the film itself, as well as the possible relevance to tissue activity of its permeability and its reactive surface phenomena.