Role of Salts in Preservation of Life 175 



With the process of hardening, or tanning, it becomes more 

 impermeable for the NaCl solution. This process of hardening 

 is brought about apparently very rapidly if we add to the m/2 

 NaCl solution a trace of a salt of a bivalent metal like Ca, Sr, 

 Ba, Zn, Pb, Mn, Ko, and Xi, etc. It is also possible that similar 

 changes take place in the whole membrane. The process of 

 rendering the m/2 Na solution harmless for the embryo of the 

 fish, therefore, depends apparently upon the fact that the addi- 

 tion of the bivalent metals renders the micropyle or perhaps- 

 the whole membrane of the egg more impermeable to NaCl 

 than was the case before. 



But these are only one part of the facts which throw a light 

 upon the protective or antagonistic action of salts. Further 

 data are furnished by experiments which I made together with 

 Professor Gies, also on the eggs of Fundulus. Gies and I were 

 able to show that not only are the bivalent metals able to render 

 the sodium chloride solution harmless, but that the reverse is 

 also the case, namely, that NaCl is required to render the solu- 

 tions of many of the bivalent metals, for instance ZnSO^, harm- 

 less. (That the SO^ ion has nothing to do with the result was- 

 shown before by experiments with Na^SO^.) 



If the eggs of Fundulus are put immediately after fertiliza- 

 tion into distilled w^ater, a large percentage of the eggs develop^ 

 often as many as 100 per cent, and the larvae and embryos 

 formed in the distilled water are able to hatch. If we add^ 

 however, to 100 c.c. of distilled water that quantity of ZnSO^ 

 which is required to render the NaCl solution harmless, all the 

 eggs are killed rapidly and not a single one is able to form an 

 embryo. If we add varjdng amounts of NaCl we find that, 

 beginning with, a certain concentration of NaCl, this salt 

 inhibits the toxic effects of ZnSO^ and many eggs are able to 

 form an embryo. This can be illustrated by the foUo^Wng 

 table : 



