BIOPHYSICAL PHENOMENA 



[PT. Ill 



salt solutions (such as o-20 M), and the hatched larvae lost relatively 

 more. 



Adolph also made a very interesting observation in the later 

 stages. Many observers had found that adult frogs gained weight 

 in dilute salt solutions, but that tadpoles lost weight in solutions of 

 the same concentration. Adolph found that there was a change 

 over as regards this property about i| days after the appearance 

 of the fore limbs, and, in his opinion, it was quite sharp. At exactly 

 the same time well-marked morphological changes occurred in the 

 skin. 



■70 



■50 



+30 



■10 



-30 



1 2 3 4 5 6 



Time in hoars 

 Fig. i8i. Embryos at the yolk-plug stage. 



"Extrusion of eggs from the body", says Adolph, "is followed by 

 a gradual increase of volume by entrance of water from the fresh- 

 water medium. Fertilisation changes all this and enables electrolytes 

 to get out of the egg so that now concentration is sacrificed while 

 volume is kept constant. Before hatching, the ability of the embryo 

 to hold its electrolytes is regained and the ability to absorb solutes 

 from a medium very dilute in them is acquired (Krizenecki). During 

 this period the ability to regulate volume is sacrificed slightly, but 

 with gain in mass it becomes possible for the larva to hold the volume 

 as well as the concentration, and the losses are exactly compensated 

 for on return to water. Soon after hatching, the tadpole is very inde- 

 pendent of its medium with respect to both concentration and volume. 

 At metamorphosis a change occurs in the mode of regulating in 



