368 CARNEGIE INSTITUTION OF WASHINGTON. 



of the hormone deemed essential for nutrition and furnished in fat- 

 free milk. 



Yeast has been shown to contain food hormones of at least one 

 type, if not more. Added to our "artificial protein-free milk," yeast 

 makes this salt-lactose mixture more efficient for nutritive purposes, 

 so that it closely resembles the highly efficient natural "protein-free 

 milk" in its nutritive potency. The use of yeast as a source of food 

 hormones will enable us greatly to extend the field of our investigations. 



As an incident to our studies of "protein-free milk" as a suitable 

 source of the essential inorganic salts, as well as certain food hor- 

 mones, for nutrition we have found that the mother liquors obtained 

 in the crystallization of commercial milk sugar and now thrown away 

 as useless waste can be made quite as effective as the laboratory-made 

 "protein-free milk" of similar origin. It would appear that in these 

 waste liquors a valuable food product has been overlooked, which is 

 destined to supplement admirably certain natural foods deficient in 

 the milk ingredients. There is no reason why this material should not 

 become available on a commercial scale. 



In continuation of more purely biological studies of growth, we 

 have demonstrated, for the albino rat, that after periods of suppres- 

 sion of growth, even without loss of body-weight, growth may proceed 

 at an exaggerated rate for a considerable period. This we regard as 

 something apart from the rapid gains of weight in the repair or recu- 

 peration of tissue actually lost. Despite failure to grow for some 

 time, the average nonnal size may thus be regained at a rate more 

 rapid than that of normal growth. 



The success of our mixtures of properly selected isolated food 

 substances as an adequate diet (as well as our caging conditions) for 

 the nutritive welfare of the rat as an experimental animal is attested 

 by the fact that we have maintained an individual in health for more 

 than three years in a small cage on a unifonn food mixture containing 

 one isolated protein (casein), starch, butter-fat, and "protein-free 

 milk"; and rats have been carried into the fifth generation on the 

 edestin diet alone. The adequate possibiUties of satisfactorily con- 

 ducting various sorts of experiments under definite and comparable 

 dietary and environmental conditions are thus demonstrated. 



Prolonged feeding with foods containing butter-fat or butter-oil 

 show the pronounced stability of the growth-promoting substance 

 contained in butter-fat under ordinary conditions of storage. How- 

 ever, in the butter "oil," in which the growth-promoting factor is 

 more concentrated than in the original fat, gradual deterioration 

 occurs, so that within a year this characteristic potency is almost 

 completely lost. 



The possession of a number of rats which had been stunted by 

 dietary procedures at a small size for very long periods of time and 



