33 2 Adaptation to Environment 



more quickly. But it is possible to make them live 

 longer in a 6/8 m solution of NaCl ; we have to proceed, 

 however, by a method which is in contrast with the 

 ideas of the adaptive influence of the environment. 

 When the fish are first treated with sea water (or with 

 a mixture of NaCl+KCl+CaCl 2 ) of a higher concen- 

 tration so that they become adapted to a 10/8 m solu- 

 tion of NaCl+KCl+CaCl 2 or to 10/8 m sea water, 

 they become also more resistant to an otherwise toxic 

 solution of NaCl. Fish taken directly from sea water 

 were killed in less than four hours when put into a 

 6/8 m NaCl solution, while fish of the same lot previously 

 adapted to 10/8 m sea water in the manner described 

 above lived two or three days in a 6/8 m NaCl solution. x 



It is not impossible that it was the high concentration 

 of calcium in the 10/8 m sea water which rendered the 

 fish more immune to a subsequent treatment with NaCl. 

 We know why a pure NaCl solution kills them and we 

 also know why the addition of CaCl 2 protects them 

 against this pernicious effect. It is rather strange that 

 where the conditions of the experiments are clear we 

 find nothing to indicate an adaptive effect of the 

 environment. 



4. Ehrlich's work on trypanosomes seems to indicate 

 a remarkable power of adaptation on the part of or- 

 ganisms to certain poisons. If the writer understands 

 these experiments correctly they consisted in infecting 



1 Loeb, J., Biochem. Ztschr., 1913, liii., 391. 



