Role of Salts in Preservation of Life 189 



to the fact that organisms are "adapted" to this mixture but 

 to a specific protective effect of the combination of the three 

 salts upon the cells. 



X 



It seems, therefore, to be a general fact that wherever tissues 

 or animals require a medium of a comparatively high osmotic 

 pressure — like our tissues — their life lasts much longer in a 

 mixture of NaCl+KCl+CaCl^ in the proportion in which these 

 salts exist in the blood and in the ocean, than in any other 

 osmotic solution, even a pure solution of NaCl. But the reader 

 has noticed that there are considerable differences in the resist- 

 ance of various organisms to abnormal solutions . While a marine 

 Gammarus dies in half an hour in an isotonic solution of NaCl or 

 cane sugar, red blood corpuscles or even the muscle of a frog can 

 be kept for a day or longer in such a solution (of course even 

 the muscle of a frog lives longer if the NaCl solution contains in 

 addition KCl or CaCl2) . What causes this difference ? 



Six years ago I found that the unfertilized eggs of the sea- 

 urchin {Strongylocentrotus purpuratiis) can keep alive and 

 remam apparently intact in a pure neutral solution of CaCl, 

 or of NaCl for several days at a temperature of 15°, while the 

 fertilized eggs of the same female are killed in a pure neutral 

 solution of CaCl., in a few hours. The same difference is found 

 for other salts also. What causes this difference? Several 

 authors have suggested that it is due to the fact that the 

 fertilized egg is more permeable to salts than the unfertilized 

 egg. But recent experiments by Warburg, which were con- 

 firmed and amplified by Harvey, make it doubtful whether the 

 salts which are not soluble in fats can enter the fertilized egg 

 at all. I believe that the explanation of the difference is much 

 more simple. The unfertilized egg is surromided by a cortical 

 layer and this layer is destroyed or modified in the process of 

 fertilization. One result of this modification is the formation 

 of the fertilization membrane, for which I have been able to 



