ROBERT F. LOEB 



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B. Rubidium Chloride Experiments. — Eggs were fertilized and 

 washed as described, and were then placed in various dishes all con- 

 taining 25 cc. of K-free sea water to which was added enough RbCl to 

 make the total concentration of RbCl in the dishes m/4,600, m/2,300, 

 m/1,300, m/850, m/660, m/550, m/470, m/370, m/330, etc., to m/18. 



The experipients proved that RbCl is entirely able to replace KCl in 

 the development of swimming blastulae and that the minimal concen- 

 tration of RbCl needed is m/660, approximately that needed when 

 KCl is used. 



TABLE I. 



Concentration of Potassium Needed for Development. 



C. Cesium Chloride Experiments. — Eggs were fertilized and wasjied 

 as described, and were then placed in various dishes all containing 

 25 cc. of potassium-free sea water to which was added enough CsCl 

 to make the total concentration of CsCl in the dishes m/4,600, m/2,300, 

 m/1,300, m/1,000, m/850, m/660, m/500, m/250, m/125, etc., to m/18. 



From Table II we see that CsCl can replace potassium chloride and 

 that the minimal molecular concentration required for this purpose 

 is practically identical for both salts. If the action of potassium is 



