288 THE UNFERTILISED EGG AS A [pt. iii 



and the word " nucleovitellin " became general, until Kossel in 1886 

 found that, if vitellin was really a nuclein, it differed from all other 

 such substances by giving no trace of xanthine after acid hydrolysis. 

 On the other hand, true nuclein, he found, was present by the tenth 

 day of development. Hall and Burian & Schur, Bessau and von 

 Fellenberg confirmed this absence of purines from the fresh egg. In 

 more recent times, Sendju and Mendel & Leavenworth have found 

 exceedingly small amounts of true nucleoprotein (2 and i*6 mgm. 

 per cent, respectively wet weight) in the hen's egg (by purine bases), 

 and Plimmer & Scott, and Heubner & Reeb have done the same (by 

 phosphorus analysis) . Shortly after Kossel's work, Milroy found that 

 vitellin gave a biuret test though no Millon, and materially differed 

 in nitrogen and phosphorus content from any of the nucleoproteins, 

 while, at the same time, Miescher admitted that he could not isolate 

 any purine bases from his "nuclein" in the hen's egg. Levene 

 & Alsberg next investigated the manner of breakdown of vitellin, 

 finding the substance they named " paranuclein " after digestion with 

 pepsin, and "avivitellic acid" after hydrolysing with ammonia. The 

 elementary composition of these substances is given in Table 10 a, 

 from which it could be seen that the increasing phosphorus content 

 implied the presence of phosphorus as an important constituent of 

 the original molecule. Six years later Levene & Alsberg ascertained 

 the amino-acid distribution (see Table 11). They pointed out the 

 significance of the high proline figure, in view of the task of haemo- 

 globin synthesis which the young embryo has before it. Abderhalden 

 & Hunter and Hugounenq undertook a like investigation in the same 

 year, from which a striking similarity between the amino-acid dis- 

 tribution in vitellin and casein came to light, especially as regards 

 the high proportion of leucine and glutamic acid. They drew atten- 

 tion to the similarity in physiological requirements as between the 

 "erste Nahrung" of chick and mammal. The historical associations 

 of this discovery have already been referred to (see p. 53). It was 

 at this time that Neuberg, and Blumenthal & Mayer reported the 

 existence of glucosamine in the vitellin molecule, two observations 

 which stood together in isolation, until in 1929 Levene & Mori 

 isolated from egg-yolk the same trisaccharide which they found to 

 be present in ovoalbumen and ovomucoid and which has been re- 

 ferred to above. 



It was not until the paper of Bayliss & Plimmer in 1906 that the 



