568 STUDIES IN GENERAL PHYSIOLOGY 
such a solution. Their duration of life after hatching is, 
however, very short. The fact that the eggs of Fundulus 
are able to develop in sea-water to which as much as 5 per 
cent. NaCl has been added shows that other constituents of 
the sea-water are able to counteract the poisonous effects of 
a pure NaCl solution. In a solution of 98 cc. §n NaCl 
+2c.c. $n KCl only a small number of embryos are formed. 
They cannot be kept alive for more than a week. In a solu- 
tion of 98 c.c. 3n NaCl+2 c.c. n CaCl, every egg devel- 
ops, but only in exceptional cases does the fish hatch. Those 
that hatch die immediately afterward. The addition of 
even as little as 4 c.c. 42n CaCl, to 100 cc. $2 NaCl causes 
all the eggs todevelop. A small amount of Ca ions counter- 
acts the poisonous effect of a large quantity of Na ions 
sufficiently to allow the development to go on, but not enough 
to allow the embryos to hatch. In a solution of 96 c.c. $n 
NaCl +2 cc, 19" CaCl, +2 c.c. n KCl not only all the 
eggs develop, but the young fish hatch and live indefinitely. 
In distilled water all the eggs are able to develop, and 
the young fish hatch in due time and live indefinitely. 
Hence the Ca and K ions of the above-mentioned solution 
are not directly necessary for the development of the fish. 
They are only indirectly necessary to counteract the poisonous 
effects of the Na ions in a solution of a Na salt. In a gly- 
cerin solution of the same osmotic pressure as a $n NaCl 
solution, no embryo was formed. In mixtures of glycerin 
and sea-water embryos formed, but the glycerin acted as a 
poison; the more glycerin the solution contained, the quicker 
it killed them. 
Thus far our results agree entirely with our previous 
results on the poisonous character of a pure NaCl solution. 
Such a solution has a poisonous effect on the germ of 
Fundulus, and the Na ions are exclusively or mainly 
responsible for the poisonous effect. But this poisonous 
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