784 BIOPHYSICAL PHENOMENA [pt. iii 



develop only in Ringer-Locke solution if removed from their enve- 

 lopes before hatching, and not at all in pond water. With regard 

 to the later rise in osmotic pressure, Bialascewicz pointed out that 

 the adsorption explanation of Backmann & Runnstrom could not 

 be right in view of the fact that the last traces of the yolk 

 disappear some time before the osmotic pressure has reached its 

 final level. On other grounds, moreover, Bialascewicz rejected any 

 association between osmotic pressure and water-content, and cer- 

 tainly the curves in Fig. 178 do not go very well together. He pre- 

 ferred to postulate an increase in osmotically active substances 

 derived from the food, and an important regulatory action on the part 

 of the kidneys, organs now (in the later stages) quite functional in 

 selectively retaining or excreting crystalloids. 



The work of Backmann and his collaborators, and of Bialascewicz, 

 was again confirmed by Przylecki, who paid special attention to the 

 role of the perivitelline fluid. In contradiction with Backmann, how- 

 ever, he found that fertilisation was not the governing factor in the 

 lowering of internal osmotic pressure in the eggs of Rana temporaria 

 and of Triton cristatus, but that this occurred whether fertihsation took 

 place or not. Absorption of water is not responsible, but rather the 

 excretion of salts and water to form the perivitelline fluid. Przylecki 

 (working on Triton taeniatus) agreed with Bialascewicz in not getting 

 such a high freezing-point as Backmann for the just-fertilised eggs, 

 i.e. — 0-20'' instead of — 0-045°. I^i a second paper, Przylecki studied 

 the conditions necessary for the formation of the perivitelHne space in 

 the unfertilised frog's tgg. The chief of these was the hypotonicity of 

 the surrounding medium, a difference in freezing-point of only a few 

 hundredths of a degree, however, being sufficient to set the process 

 in motion. The trigger mechanism is probably the entry of a small 

 amount of external water into the egg. The egg has to remain at least 

 30 minutes in the hypotonic medium, but after from 5 to 7 hours in a 

 wet chamber the eggs, placed in water, can still develop perivitelHne 

 spaces. Electrolyte solutions of all kinds hinder the formation of the 

 perivitelHne space, from A — o- 1° or o-o8° onwards. Oxygen seemed to 

 be necessary, for eggs in hydrogen and water would not produce the 

 space, although all other conditions were favourable. Augmentation of 

 10° doubles the speed with which the perivitelline space is produced. 



Work on the frog's egg was continued by Voss in 1926. By micro- 

 metric measurements he found that the size of the perivitelline space 



