ADAPTATION TO EN"VrRON"MENT — WAEDLAW 399 



attempt has been made to fix the proportion within narrow limits, 

 it seems likely that the proportion of potassium to sodium must 

 have been many times as great as it is at present. With respect 

 to these elements, the composition of those primeval seas must have 

 been considerably closer to that of the cell contents of the present 

 day than to that of the circulating fluid. 



Even when such diverse cellular tissues as human muscles and 

 herring ova are examined, the difference between the relative pro- 

 portions of sodium and potassium is not very marked. A general 

 similarity of the proportions of these elements in cellular tissues 

 is apparent. These considerations have been used to support the 

 hypothesis that the living organism has retained with remarkable 

 tenacity certain of the chemical characters imposed upon it at re- 

 mote periods of its evolution. 



THE CONCENTRATION OF THE ENVIRONMENT OF CELLS 



So far only the proportions between certain elements in living 

 tissue have been considered. It may now be asked whether the actual 

 concentrations of chemical substances present also show any relation 

 to those of the medium within which living organisms evolved 

 during a considerable period of their history. 



The most convenient single measure of the total concentration of 

 materials dissolved in a liquid is the osmotic pressure. The data 

 which have been collected by Botazzi (1908) show that osmotic 

 pressures of the body fluids of the most highly developed groups of 

 terrestrial living forms, vary only between remarkably narrow 

 limits. When different forms of sea life are examined, however, 

 a very different state of affairs is found. Even if the examination 

 be restricted to vertebrate forms, wide ranges of osmotic pressure 

 of the body fluids are met with. In the elasmobranchs, for example, 

 the osmotic pressure of the body fluids is practically that of the sea 

 water in which they live. In the teleosts, on the other hand, the 

 osmotic pressure of the body fluids differs widely from that of the 

 sea water and approaches the value found for mammalian fluids. 



Dakin (1908) has shown that the differences observable among 

 different species of fish are due to the fact that they possess adjusting 

 mechanisms of different degrees of efficiency and not to the mainte- 

 nance of specifically distinct levels of osmotic pressure. Specimens of 

 plaice taken in a brackish portion of the North Sea gave values for the 

 osmotic pressure of their blood 20 per cent lower than that of speci- 

 mens taken where the osmotic pressure of the sea water was about 

 74 per cent higher. The osmotic pressure of the blood of cod, on 

 the other hand, showed a variation of only about 3 per cent, while 



