284 THE UNFERTILISED EGG AS A [pt. iii 



old-fashioned terminology. Gobley made many quantitative observa- 

 tions on the various substances, and his figures are given in Table 17, 

 which sums up all the analyses that have been made of the yolk 

 in the eggs of birds. The original discovery of vitellin was made by 

 Dumas & Cahours, but Gobley was the first to make an extended 

 study of it. His elementary analysis is given in Table 10 a. He knew 

 that it contained both sulphur and phosphorus. Gobley was able to 

 isolate oleic and margaric (palmitic) acids from the fat fraction of 

 the yolk, but, unlike Planche twenty-five years before, he got no 

 stearic, and Kodweiss, one year later, reported its presence under 

 the impression that it had not been found before. Gobley, however, 

 was easily able to repeat Lecanu's discovery of the presence of 

 cholesterol, and made a remarkable examination of the lipoids. 

 "These viscous materials", he said, "appear to have been considered 

 by John as not being of a fatty nature at all. They form the most 

 interesting part of the yolk; they contain all the phosphorus which 

 exists there in considerable quantity." He analysed the glycero- 

 phosphoric acid which he obtained from the lipoid, which he named 

 "lecithin", and speculated as to the significance which it might have 

 for the growth of the embryo. He also recognised that fatty acids 

 and nitrogen were present in the viscous matter. 



Ten years later Valenciennes & Fremy made a further examina- 

 tion of the yolks of a large variety of eggs with special reference to 

 \itellin. It was they who discovered substances very similar to vitellin 

 in the eggs of reptiles and fishes; these they named the ichthulins. 

 As regards the eggs of birds, they contented themselves with con- 

 firming the results of the previous in\'estigators, but they regarded 

 vitellin as having practically the same constitution as fibrin, on the 

 grounds of elementary composition only. At the same time, they held 

 it to be a different compound because it would not, like blood fibrin, 

 decompose hydrogen peroxide. 



If Table 1 7 is examined, it will be seen that the yolk is much drier 

 than the white in all birds' eggs examined, having only about 50 per 

 cent, of water as against the 85 per cent, of the latter. On the other 

 hand, the percentage of fatty substances and lipoids is much higher, 

 being just about double the amount of protein, whether related to 

 wet weight or to dry. It is noticeable from the analyses of Tarchanov 

 that the yolks of eggs from nidicolous birds having a short incubation 

 time are about 10 per cent, richer in water than yolks from the eggs 



