Ion-PROTEID COMPOUNDS 553 
poisonous character of a pure NaCl solution would not have 
been possible except in a marine animal like Fundulus for 
which distilled water is not poisonous. Another possibility 
might have been the presence of a trace of acid. My 
colleague, Professor Stieglitz, was kind enough to test the 
NaCl used, for acids, but it was found to be absolutely free 
from acids. Hence I do not see any other possible explana- 
tion of the results than the theory from which we started. 
What is true for pure NaCl solutions is, of course, still 
more true for equimolecular pure solutions of KCl and 
CaCl,. They act like poisons. I have not yet been able to 
convince myself that their poisonous effect can be prevented 
by the addition of small amounts of other metal ions. 
The fact that Fundulus can be thrown from sea-water 
into distilled water without any considerable swelling, or 
without any visible injurious effects, may find its explanation 
through the influence that various ions have upon the ab- 
sorption of liquids. The above-mentioned experiments on 
the absorption of liquids by the muscle have shown that the 
simple osmotic theory of absorption which has been accepted 
by botanists cannot possibly be correct. I shall deal with 
this problem in another paper. 
III. EXPERIMENTS ON JELLYFISH (GONIONEMUS) 
The locomotion of Meduse is due to rhythmical con- 
tractions of their swimming-bell. I experimented on a 
form which is very abundant at Woods Hole, Gonionemus. 
If we put a Gonionemus into a 37 solution of NaCl, it soon 
stops contracting rhythmically. Too many Na ions take the 
place of Ca and K ions, and this alters the physical properties 
of the tissues to such an extent that no more contractions are 
possible. If such a Medusa is brought back into normal 
sea-water, it begins to beat again after a short time. In 
this case Ca and K ions take the place of some of the Na ions 
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