60 THE PHYSIOLOGY OF PROTEIN METABOLISM 



necessary to form syntonin, and so on for the other amino acids. This 

 calculated result is extremely interesting in the light of the actual 

 result. It suggests that a certain transmutation of amino acids can 

 and does take place (see later p. 61). 



Growth of Moulds. 



Some interesting work has also been carried out on the influence of 

 the nutritive medium on the growth and composition of moulds. Ab- 

 derhalden and Rona (12), for example, found that there was no apparent 

 alteration in the composition of the protein obtainable from Aspergillus 

 niger, when it was grown upon culture solutions in which the nitrogen 

 present was in three different forms : (I) potassium nitrate, (2) glycine, 

 and (3) glutamic acid. 



Variation in the Composition of Proteins. 



Another question of fundamental importance in discussing the mini- 

 mum requirement of protein, more especially in the light of Mijchaud's 

 (284) work, is whether any marked difference can be detected in the 

 constitution of proteins, obtained from different sources in the animal 

 and vegetable kingdom. Osborne and Jones (315) have carried out 

 some extremely valuable work along this line. They examined the 

 muscle obtained from chicks (312), from fish (313), and from the scallop 

 (314). When the various muscles were compared very marked differ- 

 ences in their amino acid content were found. They also showed that 

 the constitution of syntonin was very different from that of muscle 

 itself. They obtained a smaller yield of leucine, proline, phenylalanine, 

 aspartic and glutamic acids and lysine from the former. They came 

 to the general conclusion that glycine, alanine, valine, leucine and 

 proline increase in proportion as we go from the lower to the higher 

 forms of life. The table on page 6 1 copied from their paper demon- 

 strates their conclusions very clearly. 



These workers (315) have also found that the different vegetable 

 proteins differ markedly in composition. The proteins of the legumin- 

 ous seeds most nearly approximate in composition to muscle protein. 

 They suggest that this is probably the explanation why these seeds 

 have proved to be such valuable food stuffs. 1 



1 For fuller details, see Plimmer's monograph, Part I., 2nd edition in this series. 



