226 



ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1923 



comparable weight. Lactalbumin, when fed with certain nonprotein 

 constituents of milk, as in these trials, has been found to be the 

 most efficient protein of all those tested. On the other hand, for the 

 endosperm proteins of wheat contained in patent white flour, the low 

 value of 0.5 gram of gain per gram of protein consumed was ob- 

 tained. In covering the maintenance requirement of the rat, however, 

 these investigators (10) have shown that the endosperm proteins are 

 just about as efficient as the proteins of the entire grain. 



In the last five years, at the Annual Nutrition Laboratory of the 

 University of Illinois, we have conducted a large number of nitrogen 

 balance studies on rats, designed to test the comparative value of 

 the proteins from a number of foods. The results obtained have 

 been used in the calculation of biological values entirely analogous 

 to those of Thomas. We have found that when proteins are fed 

 at a low level, 5 per cent or less of the ration, the utilization of the 

 absorbed nitrogen is in general good regardless of the type of 

 protein fed. The following values represent the average utiliza- 

 tion of the absorbed nitrogen of different proteins in covering the 

 nitrogenous requirements of the body when fed at a level permitting 

 little or no growth. 



The biological value of proteins fed at a 5 per cent level 



Veal 

 Milk 

 Beef 

 Rice 



07 

 93 

 92 

 86 



Yeast 85 



Oat 79 



Coconut 77 



Corn 72 



Soy bean 73 



Casein 71 



Potato 68 



Navy bean (cooked) 29 



These figures may be taken as representing the values of the 

 digestible nitrogen from the different foods in repairing the damages 

 that the tissues sustain in the course of their endogenous catabolism, 

 whatever the nature and purpose of that process may be. Too much 

 significance, of course, should not be attached to the small differences 

 between adjacent figures in the table, although differences of 10 or 

 more are probably significant. Each figure is the average of dupli- 

 cate determinations (seven-day balance periods) on four or more rats. 

 With the exception of the proteins of the white or navy bean, the 

 proteins of the foods examined all seemed to be fairly well utilized. 

 The superiority of the proteins of milk and beef was to be expected, 

 though the high value of the proteins of rice and oats was a matter 

 of surprise. In some individual tests the proteins of rice (brown, 

 unpolished) seemed to be completely utilized. The relative in- 

 feriority of casein depends upon its low cystine content, since, by 

 the addition of cystine, its utilization could be raised above 95 per 

 cent. 



