330 THE UNFERTILISED EGG AS A [pt. m 



for he was more careful to remove all the adhering silk than was 

 Verson, and Farkas' independent work agrees rather with his. It is, 

 at any rate, clear that the shell-substance of the silkworm's egg is not 

 chitin. According to Lavini the inorganic constituents of the silk- 

 worm egg-shell are potassium silicate, sulphate, and carbonate, to 

 the exclusion of all other salts. 



The work of Pregl and of Buchtala in 1908 is perhaps the most 

 thorough investigation of the amino-acid distribution of an egg- 

 membrane protein. The figures they obtained are given in Table 

 34. The keratin of the egg-case' of Scyllium stellar e was the only 

 one of which they made a complete amino-acid analysis ; for that 

 of Pristiurus melanostoma and Scyllium canicula they only determined 

 the cystine content and large groups such as the monoamino-acid 

 nitrogen. Scyllium ovokeratin seemed to follow very closely in its 

 constitution the ovokeratin of the hen, according to the figures of 

 Abderhalden & Ebstein, which have already been discussed, but 

 separated itself off very sharply from it on account of its high tyrosine 

 content. The ovokeratin of the tortoise Testudo graeca, which had 

 been investigated two years previously by Abderhalden & Strauss, 

 was again different, having no tyrosine, but a very high percentage 

 of proline. As far as this work goes, it would seem right to con- 

 clude that, though the eggs of different species may use similar 

 proteins in their external membranes, the constitution of these proteins 

 may vary very considerably. 



The work of Steudel & Osato, and of Osato, however, brought a 

 new factor into the problem. Their analyses of the egg-membrane 

 protein of the herring's egg, which are shown in Tables 34, 38 and 39, 

 gave results which differed from the usual keratin figures, but which 

 very closely approached the analyses which they were making at 

 the same time of the ichthulin of the herring's egg. Thus the amide 

 nitrogen (2-05 per cent.) was lower than any of the keratins, but 

 approximated instead to the i-8i per cent, of herring ichthulin. What 

 appeared to be the case on a general survey turned out to be certainly 

 so when the amino-acid distribution was examined, for the two sets 

 of figures almost exactly corresponded. The properties of the egg- 

 membrane protein and the minute amount of sulphur in it precluded 

 its classification as a keratin, and the fact that no reducing sugar 

 could be discovered among its breakdown products was convincing 

 evidence against its being a mucin. Osato suggested that it was 



