NUTKITION IN MAN 343 



almost obtained with 5 to 7 grams nitrogen. The somewhat unsatis- 

 factory results were perhaps due to a partial absence of vitamines 

 (especially during the periods without yeast), or to a relatively low 

 caloric content. This was one of the few metabolism experiments 

 where the effect of such a dietary mixture on the composition of the 

 blood was studied. As to the nutritive value of bakers' yeast, 

 Hawk, Smith and Holder (1235) reported favorably that yeast can 

 replace 30 per cent of the protein of the diet. 



After this brief consideration of the protein minimum, we come to 

 the comparison between the nutritive value of vegetable and animal 

 protein. That there is a great difference in favor of the animal 

 protein, is now maintained by many, in opposition to the view held 

 by Hindhede. The present view of Hindhede was advocated many 

 years ago by Rutgers (1236). Boruttau (1237) showed in metabo- 

 lism experiments, that vegetable proteins are well utilized; he did 

 not believe that the biological value was an indication of the vitamine 

 content, for unpolished rice has a lower biological value than polished 

 rice. Botazzi (1238), on the contrary, believed in the special nutri- 

 tive value of animal protein and fat. Rose and Berg (1239) proposed 

 a view, approaching ours, in that they assumed that the protein 

 requirements depend on the nature of protein and the composition 

 of the rest of the diet. Milk protein has mostly been given an 

 exceptional place in nutrition. Recently, this was again reported 

 upon by Hart and Steenbock (1240), and we must, therefore, ask 

 ourselves the question, which chemical group in the protein molecule 

 plays such an extraordinary role in nutrition. 



This problem has been treated experimentally in such great detail, 

 that a book may well be written on the subject. For this reason, 

 we must confine ourselves to the chief results. The biological value 

 of proteins has been determined by Thomas (I.e. 1) on different 

 products and yielded the following figures: 



Beef 104 Rice 88 Peas 56 



Cow's milk 100 Potatoes 79 Wheat flour 40 



Fish 95 Casein 70 Cornflour 30 



This table is based upon the conception of the similarity of animal 

 proteins with body proteins and is due to their relative content of 

 essential amino acids. A number of amino acids have been recog- 

 nized as such. Still, in the study of the nutritive requirements of 

 the lower organisms (yeast) it has been established that some proteins 



