SECT. I] PHYSICO-CHEMICAL SYSTEM 287 



one of the main functions of the phosphatide is in furnishing phos- 

 phorus for the embryonic bones during the period of ossification, a 

 requirement which is not present in the earher stages of the develop- 

 ment. The histochemical work of Marza, who compared the white 

 and yellow yolk following the method of Romieu, is in agreement 

 with this, for he found the elements of the yellow yolk to be richer 

 than those of the white. (See Plate X.) 



1-8. The Avian Yolk-proteins 



As regards the protein, vitellin (Tables 10 a and 11), several interest- 

 ing points are to be observed. The best elementary analyses of ovo- 

 vitellin are probably those of Osborne & Campbell. After its discovery 

 by Dumas & Cahours, Gobley, and Valenciennes & Fremy, it was 

 studied by Hoppe-Seyler, and now for the first time with special refer- 

 ence to its position in the classification of the proteins. Virchow had some 

 time before then suggested that the yolk-platelets, familiar to histolo- 

 gists, contained lecithin, and there had been some doubt as to their 

 nature. Valenciennes & Fremy had opposed the view that they were 

 crystals, basing their view on Sennarmont's work, but Radlkofer and 

 Hoppe-Seyler returned to the crystal theory. Hoppe-Seyler believed 

 that vitellin contained no phosphorus, but that what appeared in the 

 analyses was due to contamination with lecithin. This view was sup- 

 ported also by his assistant, Diakonov, who contributed to the Med.Chem. 

 Untersuchungen one of the earliest investigations of phosphatide. But at 

 the same time Miescher obtained from the yolk of the hen's egg a sub- 

 stance containing a great deal of phosphorus, and possessing certain 

 of the properties of a protein. This he believed to be nuclein. "It is 

 interesting ", he said, "in relation to the origin of nuclear substance, 

 that the nutrient yolk contains ready-formed nuclein in significant 

 quantity." At this time, then, the proteins of the yolk were believed 

 to be ovoglobulin (for so Hoppe-Seyler called the vitellin of the 

 earlier workers) and Miescher's nuclein. Miescher himself identified 

 his nuclein as a constituent of the white yolk of the histologists, but 

 he noted that the hen's egg seemed to have no xanthine in it. 



Lehmann, Schwarzenbach and others, however, did not agree with 

 this classification, and regarded vitellin as a mixture of albumen 

 and casein. They did so not on the grounds of its containing phos- 

 phorus, but because they found that rennin would completely 

 coagulate it from its pure solution. But this attitude did not prevail. 



