604 WOLFGANG F. EWALD 



rhythm of the locomotor movements is retarded and the orien- 

 tation to hght is at length totally aboHshed, causing the animals 

 to swim about unoriented. It would therefore be hardly appro- 

 priate to attribute a positivating influence to CaCl2. In a long 

 standing tube with the source of light high above it, when normal 

 animals would gather near the surface, animals in the CaCl2 

 solution are equally distributed throughout the entire length 

 of the tube; the reaction to changes of intensity is considerably 

 diminished or disappears entirely. Nevertheless, the animals 

 live indefinitely in such a solution and swim about continuously. 

 With CaCl2 also there was no effect when it was added to iso- 

 tonic NaCl or omitted from artificial seawater. 



As in the two last mentioned salts, so in magnesium chloride, 

 the pure solution was toxic. I may recall the fact that in pure 

 NaCl solution the nauphi would not become negative. If, how- 

 ever, MgCl2 or MgS04 was added in the ordinary proportion 

 of artificial seawater to pure NaCl solution, the retarded nega- 

 tive reaction would be called forth instantly, provided the light 

 was strong enough. There is no appreciable difference in the 

 rate of negativation under the influence of a given source of 

 light between larvae in natural seawater and in the mixture 

 of sodium and magnesium solution. Apparently magnesium has 

 the opposite or antagonistic effect to sodium. It was now the 

 question, whether magnesium has in itself a negativating effect, 

 analogous to increase in temperature, or whether it merely 

 compensates the effect of sodium (potassium) if present in a 

 definite proportion to these salts. This question is answered 

 by experiments, in which magnesium chloride or sulphate was 

 added to natural seawater. In this case there is no negativating 

 effect whatever, even with the strongest concentration the larvae 

 could permanently stand (1:25). We are therefore justified in 

 assuming that magnesium acts only as a compensation to the 

 positivating influence of sodium but possesses no negativating 

 influence. This is confirmed by the experiments with artificial 

 seawater without magnesium. If the solution contains no mag- 

 nesium, the effect is similar to that of pure sodium chloride, but 

 the animals would keep no better than in pure NaCl solution. 



