ROBERT F, LOEB 



233 



tion of m/ 10,000 and in summer about m/ 100,000 thorium nitrate 

 could replace potassium in his experiments on the heart. In our 

 experiments, we fertiHzed eggs as described and after thorough wash- 

 ing in K-free sea water they were placed in dishes containing 25 cc. 

 of K-free sea water and enough thorium chloride to make the total 

 concentration of ThCU in the dishes m/200,000, m/ 100,000, m/66,000, 

 m/33,000, m/25,000, m/21,000, m/11,000, m/7,500, m/4,800, m/3,300, 

 and m/2,100. To these solutions, which were quite acid, enough m/10 

 NaHCOs was added to bring the pH between 7.2 and 8.0. In all these 



TABLE III. 



Effect of Thorium in Replacing Potassium. 



cases the Th was probably in suspension and not in true solution and 

 in the three highest concentrations of ThCU addition of bicarbonate 

 caused visible precipitation. Since Zwaardemaker's Ringer solutions 

 were also slightly alkaHne the Th in his solutions was also probably 

 in suspension, but this would not interfere with the radioactivity since 

 the radioactivity depends on the changes in the nucleus of an atom 

 and since these nuclear changes do not depend on whether or not 

 the substance is in true solution. As is seen in Table III in no case 

 where Th was used to replace K did we observe the development of 

 swimming blastulae and in all dishes disintegration occurred before 

 the sixteen cell stage was reached just as in the K-free sea water 



