THE OCEAN 175 



herring in their migrations keep to a water 

 whose concentration ranges from 3.2 per 

 cent to 3.3 per cent. 



From the constancy of the relative pro- 

 portion of the salts in sea water it follows that 

 every such constituent is subject to no greater 

 variations than the sum of all. Interesting 

 recent experiments have shown this fact to 

 be of vital consequence to living organisms. 

 Thus a host of experiments of Loeb and his 

 pupils, and of others, have demonstrated re- 

 markable toxicity in the action of pure salts, 

 physiologically antagonistic actions of vari- 

 ous pairs of salts, and peculiar advantages of 

 media containing a variety of salts in definite 

 relative amounts. 1 Of all such balanced solu- 

 tions sea water is by far the best, a condition 

 which is almost certainly due to the processes 

 of organic evolution. Herbst 2 has shown 

 that the development of the fertilized eggs 

 of sea urchins can only take place in the 

 presence of the chlorides, sulphates, and car- 

 bonates of sodium, potassium, calcium, and 

 magnesium, and in a faintly alkaline reaction. 

 Every one of these substances is essential, 



1 See the article by Loeb in Oppenheimer's "Handbuch 

 der Biochemie." 



2 Herbst, Archiv.fiir Ejitwickelungsmechanik, 5, 050, 1897; 

 7, 486, 1898; 11, 617, 1901; 17, 300, 1904. 



