796 BIOPHYSICAL PHENOMENA [pt. iii 



Similar determinations done on eggs and embryos of different ages 

 showed no change over 38 days, as seen in Fig. 186. Again, the 

 osmotic pressure, cryoscopically determined, was the same before 

 fertilisation as between the 3rd and the loth days, i.e. — 0-48°, 

 though this figure was rather lower than that found by Bottazzi for 

 the adult blood of the same species {Salmo fario), namely, — 0-567°. 

 In the case of Fundulus, also, Loeb & Wasteneys found no difference 

 in the depression of the freezing-point of the egg-contents before and 

 after fertilisation (in both cases — 0-76°). On the other hand Bogucki 

 found the A of trout eggs which had never been wetted, to be — 0-64° 

 while at the 8-12 blastomere stage it was — 0-42°. 



From all these facts, and those mentioned on p. 334 in the section 

 on Constitution, the conclusion is indicated that the factor which 

 retains in the normal egg sufficient electrolytes to keep the ovoglobulin 

 or ichthulin in solution is located 

 in the protoplasmic membrane, | 

 which, thickened at one part | 

 to form the germinal disc, ex- l^^^^ 

 tends right over the egg-surface ^ ^i 

 underneath the thick external I200 

 membrane. The crucial experi- "I ^ ^° 



, . . . "180 



ment to test this view as against S 

 the Moore-Osborne-Donnan I 'r 

 theory was to dialyse the egg- p^g jge. 



contents in a parchment thim- 

 ble. If the electrolytes were retained in the egg by chemical affinities 

 alone, they should not pass out into the dialysate. But experiment 

 showed that that was just what they did, giving the curves shown 

 in Fig. 187. The protoplasmic egg-membrane, therefore, cannot be 

 merely impermeable to colloids and permeable to electrolytes, but 

 must possess a certain degree of impermeability to the latter. 



The actual process of elimination of electrolytes into the sur- 

 rounding water by injured trout eggs was investigated by Gray in 

 a subsequent paper, using Blackman's exosmosis apparatus. The 

 electrical conductivity of the external medium was measured. The 

 curve resulting was sigmoid, presumably because during the first 

 period the cell-membrane was breaking down, and during the 

 second period the electrolytes were diffusing away according to 

 simple laws. 



lisation Days development of trout 



