Presence of a growth stimulating substance in the yolk of incubated hens' eggs.

Abstract

It has been shown by Burrows 1 that body cells can grow independently only when they are crowded together into narrow stagnant confines. These conditions are important because this growth depends on the accumulation of growth stimulating substance or substances to a certain concentration. This substance or substances has been called the archusia. The cells cannot retain it as it is soluble in the circulating fluids of the body. It can be extracted from actively growing tissues, and when added in sufficient quantities to the medium of a tissue culture it causes growth in cells not already containing a sufficiency of it for their growth.

Burrows finds that the blastomeres of the chick and frog embryos cannot form under the same conditions sufficient stimulus for their growth when crowded into a culture medium. For them to grow they must obtain an extra supply of stimulus from other sources. This made it seem certain that the egg must either contain a large quantity of stimulus, or such must be liberated early in its development. The failure for these blastomeres to grow under the same conditions as those suitable for the cells of older embryos, is to be related to the presence of yolk in the blastomeres. This inhibiting action of the yolk has been further associated with the presence in the fat and proteins of the yolk of a lipoid substance which has been called the ergusia. The source of the stimulus for the blastomeres has not been determined. The question arises may it not be contained in the yolk, but its action is overshadowed by the lipoids present there. Carrel and Baker 2 have shown that the lipoid of the egg inhibits growth in the tissue culture.