78o 



BIOPHYSICAL PHENOMENA 



[PT. 



20th day at the latest, and this rise was accompanied by the rise in 

 osmotic pressure. Backmann & Sundberg regarded this finding as 

 very significant, reveahng as it did something of the mechanism by 

 which the water-content of the embryonic cells was raised in the 

 later stages. The entry of the water was, they thought, the factor which 

 assured the maintenance of osmotic pressure within reasonable Hmits, 

 as the safine ions, and perhaps other crystalloids, passed into solution 



o Osmobic pressure 



(Backmann &Runnstrbm 

 Backmann & Sandbergl 



• % Water (Schaper) 

 o %Waber (Davenport) 



Fertilisation 



20 30 



Days after fertilisation 

 Fig. 178. 



from the adsorbed condition. Backmann & Sundberg found that if 

 unfertilised eggs of Rana temporaria were placed in distilled water there 

 was no sudden fall of osmotic pressure as in the fertilised eggs, but 

 a gradual swelling due to water-absorption and a decrease of A 

 from — 0-48° to — 0'35° in 3 hours, i.e. to the stage reached normally 

 by embryos by about the 20th day of development. This showed that, 

 whatever the explanation of the normal behaviour might be, it was 

 not due to simple absorption of water. From these premises it was 

 to be expected that organs or tissues of frog embryos would react 

 differently to salt solutions, if taken from different developmental 



