EFFECT OF IONS UPON TISSUE 567 



able to live for several days in sea-water to which 2-4 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 01 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 ^ n NaCl solution all the newly fertilized eggs 

 may form an embryo. Some of the embryos even hatch in 



