The rôle of alkali in the development of the sea-urchin

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 concentration 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.