262 EXPERIMENT STATION EECOED. 



genetic amino acids of the proteins in each case bear to the total amino acids, 

 as actually determined by hydrolysis. . . . 



" The amounts of glucose yielded by the metabolism of proteins stand in no 

 obvious relationship to their ability to promote growth. . . . 



"Vegetable and animal proteins under optimal conditions are metabolized 

 at the same rate in the animal organism. All the extra glucose and nitrogen are 

 eliminated by the ninth hour after ingestion." 



The influence of the plane of protein intake on growth, E. V. McCollum 

 and Marguerite Davis (Jour. Biol. Chem., 20 {1915), No. 3, pp. 415-^28, figs. 

 i2).— Laboratory animals (rats) were fed a ration consisting of dextrin, butter 

 fat, and varying amounts of skim-milk powder, for which was substituted in a 

 part of the experiments wheat protein, wheat embryo protein, and egg protein. 

 A number of curves are given to show the influence of protein intake on growth. 



The results of these tests may be summarized in part as follows : " The lowest 

 plane of protein intake derived from milk which can maintain young rats with- 

 out loss of body weight is 3 per cent of the food mixture. There is a pro- 

 gressive increase in the rate of growth with rations derived from milk, as the 

 plane of protein intake is raised between 3 and 8 per cent of the diet, . . . 



" For a time at least rats may grow at about half the normal rate when the 

 protein is supplied by the wheat kernel to the extent of 6 per cent of the food 

 mixture. 



" Two and forty-five hundredths per cent of protein derived from desiccated 

 egg is not sufficient to maintain young rats without loss of body weight. 



"During six weeks a ration carrying but 4 per cent of protein from wheat 

 embryo compares favorably with a similar plane of protein intake derived from 

 milk powder, and is somewhat better than 6 i>er cent of protein from the entire 

 kernel. 



" This plan of exi>erimentation [is believed to offer] a valuable method of 

 comparison of the proteins from various sources, provided all deficiencies are 

 made up by suitable additions." 



The comparative nutritive value of certain proteins in growth, and the 

 problem of the protein minimum, T. B. Osborne, L. B. Mendel, et al. (Jour. 

 Biol. Chem., 20 {1915), No. 3, pp. 351-378, figs. 10).— In continuation of previous 

 work (E. S. R., 31, p. 558), relative to the importance of amino acids in mainte- 

 nance and growth, the authors report further feeding experiments with labora- 

 tory animals (rats). The diet used contained protein-free milk and milk fat 

 with varying amounts of casein, edestin, lactalbumin, and several other proteins. 



It was found that growth could be facilitated or repressed at will by the 

 addition or withdrawal of cystin from a diet containing 9 i>er cent of casein. 

 With only 9 per cent of lactalbumin in the food, growth was about normal. This 

 protein contains both lysin and tryptophan in relative abundance, which it is 

 thought make up a more perfect balance in the proportion of the amino acid 

 groups essential to nutritive efficiency. 



It would seem from these and similar observations that the- amino acid 

 content of proteins is an index of the comparative values of these proteins as 

 nutrients in gi'owth. The required minimum of the protein lowest in its yield 

 of any one amino acid essential to maintenance or growth may be expected to 

 exceed greatly that of some other protein containing an abundance of the neces- 

 sary amino acid. 



Further observations of the influence of natural fats upon growth, T. B. 

 Osborne, L. B. Mendel, et al. {Jour. Biol. Chem., 20 {1915), No.. 3, pp. 379-389, 

 figs. 6). — In previous experiments (E. S. R., 31, p. 560) the authors have ob- 

 served that if rats are given a ration consisting of isolated and purified pro- 



