Some evidence of the existence of a further factor necessary for growth of the rat

Abstract

Rats often cease to grow even though they are receiving a diet hitherto considered satisfactory in calorific value, salt content, and digestibility and also containing in abundance all recognized vitamins. Resumption of growth in these animals was first obtained by substitution of "light-white casein" (B.D.H.) for the "vitamin-free casein" (Glaxo) generally used in the basal diet. Other substances which bring about rapid resumption are fresh milk, lettuce, fresh and dried grass, ox muscle, liver and wheat embryo. Less rapid growth is brought about by watercress and milk which has been simmered for 15 min. Butter and etiolated wheat shoots show very little influence on the growth of these rats. The power to cause growth resumption is removed from "light-white casein" only with difficulty. Heat can destroy it, at least partially. Cold alcohol, ether, and 2% acetic acid give inactive extracts and leave unimpaired casein. Boiling alcohol and ether give slightly active extracts and leave definitely impaired casein. The loss may be due to heat. Boiling alcohol (90%) and ether give extracts of wheat embryo of definite activity and leave the wheat embryo with only slight activity. The results here described indicate either the existence of a growth-promoting factor hitherto unrecognized or a biological inadequacy of the protein supplied to the rats in the basal diet. The preparation of active alcohol and ether extracts supports the former view.