NUTRITION. 365 



NUTRITION. 



Osborne, T. B., and L. B. Mendel, New Haven, Connecticut. Continuation 

 and extension of work on vegetable proteins. (For previous reports see 

 Year Books Nos. 3-14.) 



Our recent experiments corroborate the belief that different proteins 

 have unlike physiological values in nutrition. The most important 

 method of demonstrating this determines the minimum of each protein 

 required for nutritive equilibrium. Earlier experience indicated differ- 

 ences in the relative nutrient efficiency of different proteins — inequalities 

 which formerly were not taken into account in the practice of feeding. 

 Our experiments were limited by the quantitative inequalities of the food 

 ingested by the experimental animals. 



Further maintenance experiments consequently were undertaken, 

 in which the daily food intake was limited to a fixed quantity, the 

 protein concentration being adjusted until no essential gain or loss 

 of body-weight ensued. The absolute intake of the added protein 

 per gram of animal per week established a protein minimum for 

 maintenance in each experiment. Comparisons have been made in 

 this way at different levels of body-weight, so that the factor of size 

 might be taken into account. The total energy intake was suffi- 

 ciently Uberal to permit considerable growth had the supply of 

 protein been sufficient. In addition to the adequacy of the fats and 

 carbohydrates, the inorganic constituents as well as the food ''acces- 

 sories" were fed in absolutely the same amount daily. The added 

 protein thus represented the only important variable in the experi- 

 ments which were in all cases sufficiently long to justify a decision 

 regarding a permanent gain or loss of body- weight. The results fully 

 justify our earlier conclusions, particularly regarding the nutritive 

 superiority of lactalbumin. 



It may be expected that where growth is involved the inequaUties 

 between the different proteins would more readily manifest themselves. 

 The difficulties of ascertaining the protein minimum for growth are 

 decidedly greater than for maintenance; for by growing, the animal 

 alters its needs from day to day so that it is not easy to establish a 

 unit of comparison. It is then essential to make comparative studies 

 of growth under conditions in which the total caloric intake, the 

 absolute amount of protein eaten, the quantities of inorganic salts, 

 or amount of "food accessories," are strictly comparable. 



In one series of trials the experiments were varied in respect to the 

 protein of the diet. The food intake was so adjusted that in any 

 event there would be no unnecessary surplus of food ingested. The 

 rats — all males — were of approximately the same body-weight (45 to 

 50 gm.) at the beginning of the experiment. The trials were begun 

 with lactalbumin, edestin, and casein, the latter alone or with addi- 

 tions of cystine or alanine. The period of comparison in this series 



