SECT. 6] OF THE EMBRYO 88i 



measurements, which have already been referred to above, led 

 Vladimirov to the same conclusion. After the 6th day, there is little 

 or no change in the osmotic pressure of the egg-white. Finally, he 

 examined the pH of the egg-white at different stages, with the results 

 which have already been described (see Fig. 211). His pH measure- 

 ments were done after removal of carbon dioxide by bubbling of 

 hydrogen and subjection to a vacuum, so that the acid responsible 

 for the decreasing pH of the white must have been a fixed one, and 

 could not have been simply CO2 . Thus the tendency towards the 

 acid side of neutrality, brought about by the presence of this un- 

 known acid in increasing concentration, would lead, Vladimirov 

 argued, to a closer approach to the isoelectric point of the egg-white 

 proteins (between pH 5-0 and 6-o), and therefore to a loss of the 

 power they possess of holding water, their "Quellungsfahigkeit". In 

 this way the current of water yolkwards may be better explained. 

 It should be noted that all the constituents of the white pass into 

 the yolk or the embryo, but that when they do so at a much greater 

 rate than the average we speak of a yolkwards current. Thus the 

 salts also pass into the yolk, but not faster than the protein of the 

 white is itself absorbed by the embryo. 



Bartelmez & Riddle published some data which add to our know- 

 ledge of the current of water. The following table is striking : 



They pointed out that, as far as the fowl was concerned, the time of 

 most rapid absorption of water by the yolk was before laying, and 

 they suggested that probably the liquid which fills the sub-germinal 

 cavity in the bird's tgg was derived from this source. Digestion of 

 the upper part of the latebra would play a part in the production 

 of the sub-germinal cavity, as was first made likely by Patterson, 

 and it is a remarkable coincidence, if no more, that the cavity is 

 formed during the period of most rapid water absorption. Bartelmez 



