586 



STUDIES IN GENERAL PHYSIOLOGY 



This was indeed the case. In a mixture of 96 c.c. -|n NaCl 

 + 2 c.c. f n CaCl 2 + 2 c.c. n KC1 the eggs not only reached 

 the blastula stage and swam around in the most lively way, 

 but they reached the gastrula and even pluteus stage, with 

 the exception, however, that practically no skeleton was 

 formed. Such larva? lived for about ten days in this solution ! 

 We might think that the NaCl is an indifferent substance, 



o 



and that the Ca and K ions are responsible for the effect. 

 From what has been shown in the foregoing papers of this 

 series it follows that this assumption is erroneous. The 

 same can be proved again directly for this case. I had cane- 

 sugar and glycerin solutions prepared of the some osmotic 

 pressure as a f n NaCl solution. Table I gives the results of 

 a series of experiments. 



TABLE I 



The results could not be more striking. MgCl 2 is more 

 favorable for the segmenting egg than NaCl, but still with 

 the addition of Ca and K ions not an egg segments! These 

 experiments prove once more that the conception formed in 

 the previous papers is correct, namely, that a pure NaCl so- 

 lution is poisonous, and that it requires a small amount of 

 both Ca and K ions to antagonize the poisonous effect of a 

 NaCl solution. It seems that for the egg of a sea-urchin the 

 three metal ions in the above-mentioned proportion give the 

 colloids those physical properties which allow them to go 



