586 SruDIES IN GENERAL PHYSIOLOGY 
This was indeed the case. In a mixture of 96 c.c. $n NaCl 
+2 cc. $n CaCl, + 2 ¢.c. $n KCl 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 larve lived for about ten days in this solution! 
We might think that the NaCl is an indifferent substance, 
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 asa 37 NaClsolution. Table I gives the results of 
a series of experiments. 
TABLE I 
Character of Solution How, Sa es 
Bhi atchens 96 c.c.§2 NaCl + 23n KC1+ 219 n CaCl, | Pluteus (without 
skeleton). 
D acess 96 c.c. 49 n MgCl,+ ee + « Unsegmented. 
B sniaiids 9ec. gn LICL + He + “s Mostly unseg- 
mented, few 
reach the 2-cell 
stage. 
y eee 96 c.c. cane sugar + a + fe Unsegmented. 
Ds sevens 96 c.c. glycerin + fs + Unsegmented. 
The results could not be more striking. MgCl, 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 
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