778 



BIOPHYSICAL PHENOMENA 



[PT. Ill 



have to be reversible. Whatever the mechanism, the facts showed 

 that in its earliest stages the frog's egg was poikilosmotic, becoming 

 homoiosmotic as it developed; a conclusion of general interest in 

 view of all the work reviewed in the last section, which demonstrates 

 a passage from poikilothermicity to homoiothermicity in the case of 

 embryos during their development. 



In later papers Backmann & Runnstrom extended their researches 

 at length. They found that amphibian eggs would not develop 



a Bialascewic3 A (°) 



© Backmann Si.as80ciabes A (°) 



• Davenport water content 



■ Schaper ?> >' 



•^90 



70 - 



50- 



•2 2 

 Fertilisation 



10 12 14 16 

 Days 



Fig. 177. 



22 24 26 28 30 



normally in solutions isotonic with adult serum or ovarial egg- 

 contents, a strong indication that the behaviour of the osmotic 

 pressure with time was a physiological phenomenon. This behaviour 

 they studied at shorter intervals, and obtained the curves shown in 

 Fig. 177. The isotonicity of the freshly fertilised egg was maintained, 

 they found, during the formation of the blastula, and through 

 gastrulation, but a rise occurred in the late period of the latter, con- 

 tinuing steadily for some time until the osmotic pressure reached 

 about half the final value. Here there was a change in the rate 

 of increase, which became much slower. Neither the closure of 



