Abstract
Except for a few cases of successful cultivation in chemically defined media of special types of cells as recently reported by Healy et al. (1955) and Evans et al. (1956), it is generally the case that separated animal cells can not be grown in vitro without such materials of living origin as embryo extract or serum. The effect of embryo extract on growth of chick embryonic fibroblasts in tissue culture was first noticed by Carrel (1913) . Fischer et al. (1943) analyzed embryo extract by dialyzation and later referred to the effective nondialyzable fraction as embryonin, supposing the essential substance to be nucleoprotein (Fischer et al., 1948) . This supposition was validated by later investigations carried out by Davidson et al. (1945), Hoffman et al. (1951), Kutsky (1953), Katsuta et al. (1954) and many others, the growth-essential substance being proved to be nucleoprotein. These works chiefly pursued the efficacy of embryo extract on chick embryonic fibroblasts. On the other hand, however, Sanf ord et al. (1952) tested ultrafiltration-treated fractions both of chick embryo extract and of horse serum on the mouse L strain cells and demonstrated that the protein-containing fraction of chick embryo extract could be eliminated from culture fluid without losing the growth-promoting effects. It is thus considered that the manner in which embryo extract works for cell growth in vitro is variable according to the cell type.
In the present experiments was studied the role of chick embryo extract on the HeLa strain cells originated from a human epidermoid carcinoma of the cervix, on the basis of estimation of cell population, and it was found that the embryo extract was not essential for the cell proliferation but exerted a certain effect on the growth mode of cells.
