NUTRITION. 



367 



lent to 3 per cent of the casein used, effected considerable economy, 

 as shown in the table below. We thus see that the addition of cystine 

 rendered the casein so much more efficient for growth that, on the 

 average, 18 per cent less protein produced 12.5 per cent mxore growth. 



We have pubUshed additional experunents with tryptophane and 

 lysine which afford an important illustration of the ''law of minimum" 

 applied to essential nitrogenous components of the food supply. 



Our experience regarding the comparative value of different 

 proteins and a knowledge of the need of certain accessory substances, 

 ''vitamines," or "food hormones," such as are present, for example, 

 in our "protein-free milk" and in butter- fat, having given us an 

 insight into the essentials of nutrition, we have been in a position to 

 extend the series of experiments undertaken to determine the value 

 of several of the widely used concentrated feeding stuffs and briefly 

 referred to in our last report. 



The by-products rich in protein which are used extensively for feed- 

 ing domestic animals have heretofore been valued solely on the basis 

 of the amount of protein which they contain, no attention having been 

 paid to the qualitative character of the protein. In feeding a diet of 

 which corn or corn meal forms the chief constituent our experiments 

 indicated that better results would be obtained if the corn protein 

 were supplemented by one rich in tryptophane and lysine. Thus 

 economies can be effected by using proper combinations of these 

 relatively expensive food products. Comparisons ah-eady have been 

 made by this method of such products as distillers' grains, brewers' 

 grains, wheat gluten, cottonseed flour and meal, fish meal, beef meal, 

 soy-bean floiu- and meal, and other leguminous meals rich in protein. 

 The results obtained appear to fully justify a continuance of these 

 investigations and their extension to other largely used commercial 

 products. 



Our results with cottonseed products have especial interest, since 

 they give no evidence of any trace of toxicity in the commercial 

 preparations of flour and meal which we have used. They also 

 indicate that the proteins of cottonseed supplement those of corn 

 most efficiently, so that products containing these can be more 

 economically used when combined. In experiments in which the 

 inorganic components of the diet were furnished by our "artificial 

 protein-free milk" there was no failure of growth when cottonseed 

 flour was used, thus suggesting that the latter contains the equivalent 



