Alkali in the Development of the Sea-urchin. 119 



quantities sufficient to instantly destroy the enzyme does not pre- 

 vent reversion. Unusual interest is attached to the starch-dextrin 

 reversion, not only because of the phenomenon per se, but also be- 

 cause it is not enzymic, and because formaldehyde prevents it. 

 How formaldehyde is effective is problematical. 



74 (484) 



The role of alkali in the development of the sea-urchin. 

 By JACQUES LOEB. 



In a former paper (1898) I have shown that the velocity of 

 development of the eggs, is within certain limits, a function of the 

 concentration of the hydroxylions in the surrounding solution ; and 

 I pointed out the probable connection of the action of bases with 

 oxidations. In a later paper (1906) it was shown that at a con- 

 centration of hydroxylions below, but very close to, the point 

 where neutral red indicates an alkaline reaction (i. e., near the point 

 of neutrality) the eggs cannot develop beyond the eight cell stage. 



If we put fertilized and unfertilized eggs of Purpuratus into sea- 

 water to which a drop of neutral red has been added, at first, the 

 fertilized and unfertilized eggs take the stain equally well. If we 

 later transfer the eggs into seawater which is free from neutral red, 

 the fertilized eggs gradually take all the stain while the unfertilized 

 eggs become in the same measure decolorized. The explanation 

 for this phenomenon lies in the fact that in the fertilized egg the 

 neutral red enters into a chemical combination by which it becomes 

 undiffusable ; while in the unfertilized egg the neutral red is only 

 held in solution. Since neutral red is a base it is to be presumed 

 that the body in the egg with which it combines is an acid. 



This suggested the possibility that the above mentioned accel- 

 eration of the development of the egg by other bases, e. g., sodium 

 or potassium hydroxide, might be due to a combination of these 

 bases with the same acid with which neutral red combines in the 

 fertilized egg. If this assumption were correct it should be ex- 

 pected that the addition of two or three drops of a 1/100 gram- 

 molecular solution of neutral red to a neutral van't Hoff solution 

 (in which the fertilized eggs cannot develop) should cause the eggs 

 to develop into swimming larvae. The experiment was tried and 

 it was found that neutral red has indeed such an effect. 



