332 EDWARD F. ADOLPH. 



all the freshwater animals studied, toxic effects followed immer- 

 sion in a concentration of about 0.35 M non-electrolyte solutions, 

 or the equivalent concentration of electrolytes. Fredericq ('98) 

 and Botazzi ('08) have shown that the tissue fluids of freshwater 

 animals always have osmotic pressures less than half of that of 

 sea water (A = 0.8 C.), and usually have only one eighth to 

 one fourth of that of sea water; while marine animals have body 

 fluids which are exactly isotonic with sea water. We can thus 

 probably regard the maximum survival concentration for fresh- 

 water animals as a measure of the osmotic pressure of their 

 body fluids. All the freshwater animals studied* evidently had, 

 therefore, internal osmotic pressures equivalent to 0.20 to 0.35 M. 



The acclimatization of marine organisms to changed osmotic 

 conditions contrasts to that for freshwater organisms. In several 

 instances marine animals placed in glass-distilled water died, yet 

 most of them survived a mixture of 98 or 99 per cent, of distilled 

 water with only 2 or i per cent, of sea water. In other words, 

 most marine animals are able to live after abrupt change to 

 almost pure fresh water, providing that the remaining salts are 

 present in physiological proportions. Gradual dilution of the 

 sea water over several days did not materially help marine 

 animals to endure pure water, though complete acclimatization 

 has been secured over long periods of time by other observers 

 (Beudant, '16, Plateau, '71, Semper, '80). 



For freshwater organisms, gradual increase in the concentration 

 of the medium did not greatly increase the maximum survival 

 concentration. It is evident from this that plasmolytic effects 

 are not the important ones in producing this toxicity. In diluted 

 sea water all the freshwater animals studied except Gammarus 

 were killed in concentrations less than half of that of the sea- 

 water at Woods Hole (A = 1.8 1 C.), and acclimatization never 

 increased this toxic limit up to half of the concentration of the 

 sea water. Similar acclimatizations to specifically poisonous 

 substances have been demonstrated by Davenport and Neal 

 ('96) and numerous other investigators, so that it seems doubly 

 certain that the ultimate toxic effect is not plasmolytic. More- 

 over, the toxic effect cannot be attributed to sudden volume or 

 concentration changes such as are brought about by diffusion. 

 Certain balanced solutions such as sea water can be resisted in 



