560 EXPERIMENT STATION EECOED. 



casein, and edestin, respectively, it will be seen tliat " this small addition of lac- 

 talbumin lias furnished all the factors required for normal growth. This protein 

 mixture therefore undoubtedly contains sufficient tryptophan and lysin to 

 satisfy the normal requirements of the growing animal. Since casein yields 

 nearly as much lysin as does lactalbumin, we assumed that the failure of an 

 equal addition of casein was due to a relative deficiency in tryptophan." That 

 this assumption was true was shown by experimental evidence. " Similarly 

 we assumed that the failure to grow on the comparable zein+edestin food was 

 caused by the relatively small amount of lysin yielded by edestin." 



Here, too, the experimental evidence showed the correctness of the assumption. 

 " These experiments are further of chemical interest in indicating, as the result 

 of this biological test, that edestin is richer in tryptophan than casein — a fact 

 hitherto unappreciated. 



" The growth of rats on a food of zein+ lysin + tryptophan has not always 

 been as rapid and prolonged as we might expect. We are by no means prepared 

 to maintain that the final solution of the proportion of amino acids requisite 

 for the growth of rats has been determined. Newer trials may indicate the 

 desirability of increasing the proportion of argiuln present in zein foods; and 

 still other adjustments may be required^ to promote ideal growth in this or 

 different species. The way to successful investigation has been opened." 



The influence of cod liver oil and some other fats on growth, T, B. 

 Osborne, L. B. Mendel, et al. {Jour. Biol. Chem., 11 (Wl^), No. 3, pp. 401- 

 408, figs. 4)- — The inability of laboratory animals (young albino rats) to 

 complete their growth on a diet consisting of isolated proteins, starch, protein- 

 free milk, and commercial lard, called attention to the need for supplying 

 some other substances in order that growth might proceed to its normal 

 limits. 



As was pointed out in earlier experiments (E. S. R., 30, p. 560), the lacking 

 factor was found in the fat component of milk, a conclusion substantiated by 

 later investigations. A ration consisting of 18 per cent purified protein, 26 

 per cent starch, 28 per cent protein-free milk, 10 per cent commercial lard, 

 and 18 per cent butter fat, the authors state, appears to be in every way ade- 

 quate for the continued nutritive needs of the species experimented with. 

 Some other fats have been found to behave like butter fat in this respect — for 

 instance, egg yolk fat (E. S. R., 29, p. 664). The authors state that they have 

 likewise obtained uniform success when cod liver oil was substituted for a 

 portion of the lard in the standard diets. On the other hand, it was observed 

 that almond oil uniformly failed to restore growth when it had ceased on the 

 usual lard-food mixtures. 



" We have already pointed out that it seems improbable that the triglycerids 

 of the fatty acids ordinarily present in foods are responsible for the favorable 

 effects noted. If they were, there is no apparent reason why such fats as 

 commercial lard and almond oil should be ineffective. Experiments as yet 

 incompleted have made it clear that the growth-promoting substance is not 

 present in the more solid fractions of butter fat which constitute about one- 

 half of it and are at least soluble in alcohol at low temperatures. 



" It is perhaps more than a mere coincidence that cod liver oil has so long 

 enjoyed a reputation for nutritive virtues which can scarcely be attributed 

 to its fat content per se. At one time its therapeutic value was ascribed to 

 the small proportion of iodin which it is known to contain. This explanation 

 has, of lale, been replaced by the suggestion that the special potency of cod 

 liver oil resides in the peculiar fatty acids which it contains. . . . 



" Perhaps experiences such as have been reported in this paper will pave 

 the way for a clearer understanding of Uie i)hysiological potency of natural 



