1056 PROTEIN METABOLISM [pt. iii 



Over the whole period the percentage of amide and humin nitrogen 

 showed no change, except a very slight decrease in amide nitrogen 

 in one experiment. The total di-amino nitrogen percentage, however, 

 increased to the extent of 2 per cent., and, corresponding with 

 this, the arginine nitrogen increased by i per cent. Histidine and 

 lysine probably account for the difference. Conversely the mono- 

 amino-acids decreased — from 64-0 to 60-2 in one experiment, and from 

 63-7 to 62-8 in another. The non-amino nitrogen of this fraction, on 

 the other hand, increased, and, as far as could be ascertained with these 

 methods, the cystine nitrogen did so too. As the figures for bromine 

 absorption decreased continually through development, Plimmer & 

 Lowndes suggested that the cystine was increasing relatively at the 

 expense of tyrosine, but, as Plimmer & Phillips had previously shown, 

 the bromination method is not very quantitative, nor even very 

 specific. The main result of the investigation was the finding that 

 the mono-amino-acids decreased and the di-amino-acids increased, 

 with the suggestion that the former were those principally used for 

 furnishing energy by combustion. As will be mentioned later, an 

 analogous process seems to go on in the eggs of the trout and the 

 salamander, the only other material which has been treated from 

 this point of view. 



Very similar experiments to those of Plimmer & Lowndes were 

 carried out by Russo, whose main interest lay in the origin of the 

 purine bases. He had already found a diminution in the arginine 

 and histidine content of the echinoderm testis corresponding to 

 an increase in the purine bases, and, in accordance with the 

 original suggestion of Hopkins & Ackroyd, he was inclined to 

 regard that way of derivation as universal. Russo's results with 

 avian eggs are shown in Table 131; they were obtained with the 

 van Slyke method applied to the massed proteins of all the parts 

 of the egg-contents. It is evident from the figures that in his experi- 

 ments the amide nitrogen remained constant (agreeing thus with 

 those of Plimmer & Lowndes) , as also did the cystine (differing from 

 theirs) . Russo's treatment of the cystine question, however, cannot 

 be considered final, for, as Plimmer & Lowndes have shown in 

 another paper, some of the cystine passes into the filtrate from the 

 phosphotungstates of the hexone bases in the van Slyke method, 

 and must be looked for there. The question is also complicated by the 

 presence of Mueller's sulphur-containing amino-acid in the mono- 



