602 WOLFGANG F. EWALD 



I will next discuss the influence of the salts of the seawater on 

 phototaxis. In this connection I desire to express my thanks to 

 to Dr. 0. Meyerhof, who gave me many valuable hints. Acting 

 on his advice I used 0.65 molecular solutions which corresponded 

 best to the concentrations found in the Naples Aquarium water 

 at the time. I made up solutions of chemically pure sodium 

 chloride, potassium chloride, magnesium chloride, magnesium 

 sulphate and calcium chloride. The magnesium and calcium 

 chloride were tested by titration. The effects of the different 

 salts were studied firstly by adding them to pure isotonic sodium 

 chloride solution, secondly by adding them to natural seawater 

 and finally by eliminating successively each component salt from 

 artificial seawater made up of the five components mentioned, 

 with the addition of the necessary amount of alkali. The arti- 

 ficial seawater had the following composition: 



0.65 mol. NaCl ! .100.0 



0.65 mol. KCl 2.2 



0.65 mol. MgClo 6.6 



0.65 mol. MgS04 4.2 



0.65 mol. CaCIo 2.0 



1 .00 mol. NaHCOa 0.25 



0.10 mol. NaOH 0.2 



The amount of alkali* is that found by Warburg at the Naples 

 Institute by comparison with natural seawater. The animals 

 kept well in this artificial seawater, if not quite as long as in 

 natural seawater. There was no effect on phototaxis on trans- 

 ferring the nauphi into artificial seawater. That is: the time 

 elapsing until the reverse of orientation under the influence of 

 a certain source of light was neither shorter nor longer than in 

 control animals kept in natural seawater. The artificial sea- 

 water was therefore in its influence on phototaxis equivalent 

 to natural seawater. 



When the animals were transferred into pure isotonic NaCl 

 solution, negative larvae became positive, positive larvae more 

 positive. Moreover, positive animals would not become nega- 

 tive again, even under the influence of full sunlight, including 

 the ultra-violet rays. They died after a short time through 



