SECT. 5] IN ONTOGENESIS 817 



K 



Na 



CI 



Lactate 



Other monovalent anions ... 



Free glucose 



Unknown neutral substances 



0-42 0-57 



Although their figures for ash, especially in the yolk, do not agree 

 altogether with those of other workers, yet their contention, that each 

 dissolved substance varies quite independently in yolk and white, 

 must be admitted. It is not merely that the total osmotic concentra- 

 tion of each phase is distinct but also that practically no agreement 

 exists between the constituent items in that concentration. The 

 difference between yolk and white is as much as i-8 atmospheres, 

 and if this was all due to the osmotic properties of the membrane 

 alone, it would have to support, Straub & Hoogerduyn calculated, 

 a pressure of 2 kilos per square centimetre. They considered that 

 the Schreinemaker equations were therefore inapplicable, and as for 

 those of Donnan, the distribution of ions in yolk and white was so 

 different from what would be expected according to Donnan's theory 

 that it was very unlikely it could hold in this case. 



Straub & Hoogerduyn entered a quite new field when they sug- 

 gested that the osmotic difference between yolk and white was a 

 " Lebenswirkung " in the sense that the vitelline membrane might 

 be physiologically bound up with the egg-cell or pre-gastrula. If 

 this was so then after long storage the infertile egg should show a 

 disappearance of the special membrane properties which characterise 

 it when it is fresh. They mentioned, in this connection, the ex- 

 periments of L. K. Wolff who had found that in the fresh egg 

 there is a trace of zinc in the yolk and a trace of copper in the 

 white while after storage for some time these metals are equally 

 distributed throughout the egg. Their own experiments showed 

 that eggs stored for a long time tend to acquire equal osmotic 

 pressures on both sides of the membrane : 



A n A n 



white yolk 



Fresh eggs ... ... ... ... 0-45 o-6o 



Conserved eggs ... ... ... 0-50 0-52 



Frozen eggs ... ... ... ... 0-49 0-50 



