JACQUES LOEB 



241 



Our first experiments consisted in mixing various quantities of 

 natural sea water and Li mixture to find out the maximal amount of 

 Li in natural sea water which still permitted the formation of normal 

 blastulae in about 16 or 20 hours; the eggs were put into the solution 

 immediately after fertiHzation. It was found that only 8 per cent 

 of the Li mixture could replace the natural sea water without pre- 

 venting the development of the eggs into swimming blastulae. When, 

 however, the proportion of KCl contained in the sea water was in- 

 creased thirteen times its normal amount the eggs were able to develop 

 into larvae when as much as 52 per cent of Na was replaced by Li. 

 It is therefore possible to increase the tolerance of the sea urchin egg 



TABLE III. 



Maximal Amount of Li in which Swimming Blastulm of Arbacia Can Be Obtained. 



against Li 600 per cent by increasing simultaneously the amount of K 

 normally present in the sea water by 1,300 per cent. Since it was 

 necessary to keep all the other constituents of the sea water constant 

 the KCl was not added in the form of a pure m/2 solution of this salt 

 but in the form of a mixture of the following composition which we 

 will call the KCl mixture. 



100.0 cc. of m/2 KCl 

 1.75cc. of m/2 CaCl2 

 7.8 cc. of m/2 MgCl2 

 3.8 cc. of m/2 MgS04 

 0.8 cc. of m/10 KHCO3 



Systematic experiments showed that the maximum dose of Li in 

 which the eggs could develop into larvae increased with the concentra- 

 tion of K added to the sea water. This is indicated in Table III. 



