Errect or Ions upon TIssut 567 
able to live for several days in sea-water to which 24 per 
cent. NaCl had been added. When I made these experi- 
ments I still accepted the common view that NaCl was an 
indifferent substance, and that in these experiments it acted 
only osmotically. The results of my recent work and of 
experiments to be mentioned in this paper, however, prove 
that we have to deal with the effects of Na and Cl ions in 
these experiments. It therefore follows that the Na and Cl 
ions (especially the former) are more injurious during the 
earliest stages of cell-division than during the later stages. 
I made my new experiments on the effects of various ions 
upon development on the eggs of the same form. 
If the eggs of Fundulus be put into a §n NaCl solution 
immediately after fertilization, the development stops in most 
cases at an early stage (64 to 128 cells) and only a few eggs 
form an embryo. If the development does not stop during 
the first twenty-four hours, it continues as a rule normally 
for one or more weeks. Hence a pure NaCl solution seems to 
be more poisonous during the first twenty-four hours of devel- 
opment than during the later stages. Control experiments 
verify this assumption. Eggs that were allowed to develop the 
first eighteen or twenty-four hours in sea-water, and are then 
put into a $n NaCl solution, continue to develop in almost 
every case. No embryo is able to hatch in these solutions. 
In our previous paper we showed that a young fish died 
in a few hours in such a solution. The fact that the egg 
lives longer in it may be due either to the fact that the tough 
egg membrane does not allow the ions to penetrate so fast 
into the embryo, or to the presence of the yolk which to a 
certain extent may regulate the proportion of ions in the 
embryo. 
If we dilute a $n NaCl solution with distilled water, we 
find that in a in NaCl solution all the newly fertilized eggs 
may form an embryo. Some of the embryos even hatch in 
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