FEEDING EXPERIMENTS WITH ISOLATED FOOD SUBSTANCES. 53 



SUMMARY 



The problems of nutrition have been reviewed in this paper in 

 the light of the newer knowledge of the chemical structure of the 

 proteins. The possibilities of protein synthesis in animals and the 

 conditions which this postulates ; the significance of the availibility, 

 palatability, and physical texture of the food-intake; the suggested 

 role of various accessories inorganic salts, lipoids, etc. ; the distinc- 

 tion between the nutritive demands during the period of growth and 

 those of later adult life, are brought within the range of discussion. 

 The literature on experiments in which isolated food-substances have 

 been fed to animals is discussed in some detail, with a critical con- 

 sideration of some of the essential conditions of investigation which 

 are demanded in successful research in this direction. 



The methods of metabolism study with white rats used in this 

 research are described and illustrated. Control feeding trials showed 

 that the animals can be maintained in nutritive equilibrium and 

 health for periods of many months under the conditions of experi- 

 ment adopted. The failure to eat sufficient food is indicated as a 

 cause for the unsuccessful termination of numerous experiments. 

 The facts presented exclude the probability that monotony of diet 

 is an insurmountable obstacle to nutritive success. 



Numerous experiments are reported in which casein formed the 

 sole nitrogenous constituent of the dietary. In this connection it is 

 shown that the make-up of the inorganic constituents of the diet ex- 

 ercises an influential effect on the nutritive efficiency of the dietary. 

 From the experience thus gained a "basal" ration was constructed 

 on which rats were kept many months in good health. Some of these 

 experiments in which the animals exhibited no noteworthy altera- 

 tions in weight and showed a good gain in nitrogen are, as far as the 

 authors are aware, the most successful recorded attempts at artificial 

 nutrition with a constant mixture of pure food-stuffs, containing only 

 a single protein. Satisfactory experience also followed the gradual 

 complete substitution of the casein by other proteins, one animal 

 continuing more than 217 days on a diet in which the sole protein 

 was glutenin. 



With young rats it has been possible to maintain weight with 

 dietaries like those just mentioned, although with little if any growth. 

 The limitations of the method are discussed and plans for continued 

 investigation indicated. 



January 191 i. 



