i82 PROTOPLASMIC ACTION AND NERVOUS ACTION 



scope as a clear halo surrounding each egg. When the 

 egg is washed in pure isotonic NaCl solution (0.54 m), 

 preferably with the aid of centrifuging, the jelly swells 

 and dissolves; but in NaCl solution containing a little 



CaCl2 ( — is suflSicient) it remains intact. Salts of 

 400 



several other metals (Mg, Mn, Co, Ni, Al) have been 

 found to have a similar effect.' The jelly layer, in the 

 presence of the salts of sea water and in mixtures of 

 NaCl and CaCU, thus possesses a certain water- 

 insolubility and physical consistency; these properties 

 are apparently dependent on the presence of a calcium 

 compound (possibly proteinate) with definite physical 

 properties (especially water-insolubility and lack of 

 tendency to swell) which preserves the characteristic 

 structure and consistency of the whole layer. In pure 

 NaCl solution this constituent is replaced by the corre- 

 sponding sodium compound which is water-soluble and 

 swells readily, hence the coherence and insolubility of 

 the layer as a whole are lost. 



This process may be regarded as a model of the 

 essential kind of change occurring in the plasma mem- 

 branes of living cells in pure NaCl solution. The 

 surface of the starfish egg is in fact physically altered 

 by NaCl solution in a characteristic manner; unfertilized 

 eggs placed in the pure solution cohere in clumps or 

 agglutinate; many eggs also form fertilization-membranes 

 (when returned to sea water) and show evidence of 

 partial activation by cleaving and in some cases develop- 

 ing to the blastula stage. All of these effects of the pure 



^ Unpublished experiments in the Nela Research Laboratory at the 

 Marine Biological Laboratory at Woods Hole. 



