NUTRITION. 353 



a method whereby it became possible to feed the entire seed, and thus 

 compare the untreated protein of the various grains. We are now 

 engaged in such a comparative study of barley, oats, rye, and wheat 

 as sources of protein, feeding each at different protein levels and com- 

 paring the efficiency of the growth made on each. These studies also 

 furnish information respecting the economy of protein in nutrition. 



In making such comparative tests in the past, it has been difficult to 

 interpret the results accurately, because individual animals eat different 

 quantities of food and consequently grow at different rates. In some 

 experiments we obviated this difficulty by limiting the amount of food 

 given the rats to such a quantity that all the animals grew at approxi- 

 mately the same rate, and ate practically the same amount of food 

 during the same period. The only variables were the kind and percent- 

 age of protein employed. This method was exceedingly laborious, and 

 the outcome was not entirely satisfactory. 



As a result of some of our work on the value of the proteins found in 

 the different parts of the wheat kernel, we developed a method for 

 assigning a numerical value to each protein, based on the ratio between 

 the amount of protein eaten and the gain in body-weight during a given 

 length of time, starting at approximately the same initial weight. 

 Although this method does not eliminate the individual differences of 

 the animals in their ability to utilize their food economically for main- 

 tenance or growth, nevertheless, where pronounced differences in the 

 nutritive value of the various proteins exist, the effect of these may be 

 compared by means of the numerical values thus assigned to the pro- 

 teins. For example, when wheat flour furnished all the protein of the 

 diet, the rats gained on an average only 0.5 gram of body-weight per 

 gram of protein eaten, whereas when the food contained the same 

 percentage of protein consisting of a mixture of two parts of wheat- 

 flour protein and one part of egg protein, the rats gained on an average 

 2.0 grams of body-weight per gram of protein eaten. Thus it was shown 

 that the excellent growth of the rats on the flour + egg diets, as com- 

 pared with the little more than maintenance of those animals on the 

 wheat-flour diets, was not due solely to the larger amount of food eaten 

 in the former case, but rather to the superior quality of the protein. 



Although this method of comparison and evaluation of proteins has 

 its limitations, it is proving useful in our study of the relative value of 

 the cereal proteins. It is early to draw final conclusions, but the 

 results already obtained seem to point to the probability that the 

 wheat proteins are somewhat inferior to those of barley, oats, or rye. 

 While a rat can grow to full maturity on a diet of the entire wheat 

 kernel supplemented with a suitable salt mixture and butter fat, to do 

 so requires more protein than if the ration contained barley, oats, or 

 rye as its sole source of protein. 



