Antigrowth Effect of Lipoid Fractions of Tissue Extracts.

Under the relatively simple conditions that prevail in the cultivation of cells in vitro it has been fully established that certain constituents of the tissues and fluids of the body stimulate growth and that others inhibit it. Carrel ' noted that the growth of connective tissue was more abundant in the plasma of young chickens than in that of older ones and, in I92I, Carrel and Ebeling2 determined that the influence of age, as reflected in the serum of the animal, was exerted not by variations of growth-accelerating factors, but by fluctuating inhibiting agents. Later, in I923, the same authors3 separated the serum into a growth-activating and a growth-inhibiting fraction by precipitating the former by bubbling carbon dioxide through the diluted serum. Actually to accomplish indefinite multiplication of fibroblasts in artificial mediums it is required that the inhibiting effect of the plasma be counterbalanced by the addition of positive stimuli, especially in the form of embryonic juice or primary protein dervatives.4'15 6 Very potent growth stimuli are present in the tissue of Rous chicken sarcoma. Sittenfield and Johnson7 showed that the tumor-producing substance could be neutralized by mixig an active filtrate with blood, and subsequently recovered by buffering the mixture to a pH 4.o and then extracting the resultant precipitate at a pH of 8.o to obtain the active tumor agent in solution. This substance that neutralized the tumor principle was later found by Sittenfield, Johnson and Jobling8 to be confined to the globulin fraction of serum. Information concerning the growth regulatory mechanism which operates in the living animal has been slower to appear. So far as is now known types of growth such as embryonal, regenerative, compensatory and even neoplastic, may take place in response to stimulating and re-