ION-PROTEID COMPOUNDS 555 
Medusa the same is true as for Fundulus. Na ions are poi- 
sonous in a pure NaCl solution, while the same solution is 
harmless if a certain amount of K and Ca ions are present. 
Our theory that the irritability of tissues depends upon the 
presence in definite proportions of Na, K, and Ca ions is 
once more verified. It goes without saying that a pure jn 
KCl and a pure 1 n CaCl, solution was still more poisonous 
than a §n NaCl solution. 
IV. EXPERIMENTS ON CILIARY MOTION 
The conditions for ciliary movements were studied in the 
young larve (blastula, gastrula, and pluteus) of the sea- 
urchin. The movements of these larve are due to cilia 
which are incessantly active. I found that these. larve do 
not die rapidly in a $n NaCl solution. They may live 
twenty-four hours. But if we add a small amount of jn 
KCl and 4-n CaCl,, they may be kept alive and in motion 
for ten days or more. In the latter solution their develop- 
ment can continue, while in the pure NaCl solution this is 
not possible. 
I was, however, surprised to find that this ciliary motion 
continued in solutions in which no muscular contractions of 
Fundulus or Gonionemus were possible. Larve which were 
twenty hours old were able to swim for about forty-eight hours 
in the following solutions: 
90 cc. 4 n MgCl, +10 c.c.4¢ » CaCl, 
80 +20 “ 
50 “ +50 “ 
The reader will notice that these solutions contain no NaCl. 
I tried the effects of these solutions on Gonionemus. As 
was to be expected, not one contraction was possible in these 
solutions. The following observation is equally astonishing. 
Combinations of NaCl and KCl were tried: 
(1) 80cc. $n NaCl + 20 ce. §n KCl 
(2) 20cec “ + 80 . 
Digitized by Microsoft® 
