Abstract
In a previous paper the author in collaboration with Richardson 1 described variations in the cytolytic changes occurring in undifferentiated and differentiated tissues which were induced to undergo prolonged proliferation in an unchanged medium in vitro. The present study was undertaken to extend similar comparative observations upon the rate of cytolysis in pure isolated strains of cells, each possessing different inherent growth rates. Under experimental conditions Parker and Fischer 2 depicted different strains of “Fibroblasts” possessing varying growth potencies, and, for the purpose of these experiments similar tissues were selected and isolated according to the methods described by these investigators. All tissues employed were taken simultaneously from the same embryo of 12 days' incubation and throughout this investigation were explanted under exactly identical conditions from the moment of their isolation in vitro. The selected fragments were obtained from the following regions : osteoblasts from the supra-orbital; chondrioblasts from the periostium of the sphenoid (fast growing); and fibroblasts from heart and leg muscles (slow growing).
The first cytolytic response to the accumulations of cyto-toxins in the unchanged medium was morphologically expressed in the slow growing strains after 65-70 hours incubation in vitro. Similar examinations, however, of the fast growing strains after the same periods of growth showed them to be more resistant to the factors incurring cytolysis, as degenerative phenomena were not yet apparent. Even when the fast growing osteoblasts and the slow growing muscle-fibroblasts were implanted side by side in the same culture medium, they not only showed the same relative difference in their growth rates, but exhibited the same time variations as when cultivated in their isolated conditions.
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