8i4 



BIOPHYSICAL PHENOMENA 



[PT. Ill 



many workers (Aggazzotti; Greenlee) during the first week of in- 

 cubation. That it does not entirely account for it will be apparent 

 when the work of Vladimirov and his collaborators is considered (see 

 (p. 88 1 ) . Then it must be remembered that all the points on the graph 

 in Fig. 198 are at a lower level ^(O) 

 than the A of the blood of the 

 adult hen, which Bialascewicz 

 found to be — 0-635°. The yolk 

 of ovarial eggs he found to be 



— 0-613°, and the yolk of eggs 

 from halfway down the oviduct 



— 0-585°, so that the falling curve 

 for the yolk seen during the early 

 days of incubation is simply the 

 continuation of a curve which 

 could be constructed for all stages 

 after the yolk leaves the ovary. 

 Thus, by the time the yolk has 

 arrived at the stage of being laid, 

 it is distinctly hypotonic to the 

 parent blood, as is also the white, 

 which has surrounded it. Pro- 

 cesses of some sort, therefore, 

 must be taking place, tending 

 to diminish the concentration of 

 osmotically active substances in 



the yolk. Bialascewicz supposed the yolk to absorb water as soon as 

 it came into contact with the white in the oviduct, and he regarded 

 the state of affairs at laying as an equilibrium condition, in which 

 the osmotic pressure value was regulated by the degree of stretching 

 which the elastic vitelline membrane could stand^. During incuba- 

 tion, the membrane became more extensible, and further dilution 

 of the yolk by water from the white proceeded. Bialascewicz con- 

 firmed the old observation of Harvey that the white almost entirely 

 disappears before the end of incubation, and gave a few figures,^ but 

 the most complete data showing this are some which I collected in 



5 10 



+ Yolk ) Rices, Young 

 X White /various breeds 

 Amnloticfluid j 

 © Allantoic " j 

 X White(Vladimirov) 



Kamej 



• Yolk ) g 



O White I o 



® Embryo >ra 



^ Amniotic fluid .5 

 ffl Allantoic ,■> 1'^ 



Fig. 198. 



^ The equilibrium may also, however, be chemical in origin (see p. 819). Bialascewicz 

 had no evidence for his views on the elasticity of the vitelline membrane. 

 2 See also Fangauf's data. 



