210 RUTH WitEELER 



kept his animals alive twenty-one days, though they began to 

 lose weight on the ninth day or earlier; Willcock and Hopkins,^ 

 feeding zein with and without tryptophane, carried their exper- 

 iments not longer than sixteen days; mice fed on casein with cane 

 sugar and sodium carbonate by Abderhalden and Rona,^ lived 

 about three weeks; Rohmann was able to get second and third 

 generations on a mixture of proteins^ and more recently,^ in the 

 work referred to above, on a single protein — fed with carbohy- 

 drates, fats and salts. The details are not yet available. The 

 mice fed by Suzuki, Shimamura and Odake^ on casein, lecithin, 

 starch, 'oryzanin' from rice, and salts all died within thirty-nine 

 days. 



Certain problems of nutrition can be solved only by feeding 

 experiments that extend over a considerable time and in which 

 the food substances are furnished in a purified form. Animals 

 have a surprising power of getting along for a time on a quali- 

 tatively inadequate diet. Mice kept upon a ration in which two- 

 thirds of the protein was gelatin and the other third casein did 

 not show a decline in body weight for twenty-one days, although 

 the ultimate decline of every animal fed upon this food showed 

 it to be insufficient; another group made material gains in weight 

 for seventeen days on a diet upon which all ultimately lost weight 

 rapidly and died unless the food was changed. Even more es- 

 sential for decisive results is the purity of the individual food 

 substances employed. When the composition of the food is 

 known with certainty and can be altered at will, the solution of 

 dietetic problems begins to look more possible and also vastly 

 more interesting. Differences in the nutritive properties of pro- 

 teins such as the glutenin and gliadin of wheat, for example, 

 may be altogether hidden if either retains a small amount of 

 the other. For the present work it fortunately was possible to 

 use the foods prepared for the feeding trials in the experiments 

 of Osborne and Mendel already cited. 



6 Journ. Physiol., vol. 35, p. 88, 1906. 



7 Zeitschr. f. physiol. Chem., Bd. 42, p. 528, 1904. 



8 Abstracts in Maly's Jahresbericht, Bd. 38, p. 659, 1908. 



9 Biochem. Zeitschr., Bd. 43, p. 89, 1912. 



