Adaptation to Environment 329 



fish to a higher concentration of the sea water ; whereas 

 the fish was already immune to this high concentration 

 before coming in contact with it. 



This fish seemed a favourable object from which to 

 find out how far an adaptation to the environment 

 really existed; and the result was surprising. By 

 changing the concentration of the sea water gradually 

 it is possible to raise the natural resistance of the fish 

 only a trifle, not much over ten per cent. The con- 

 centration of the natural sea water is a little over that 

 of a m/2 solution of NaCl+KCl+CaCU in the pro- 

 portion in which these three salts exist in the sea water. 

 When adult Fundulus are put into a 10/8 m solution 

 of NaCl+KCl+CaCU in the proportion in which these 

 salts occur in sea water they die in less than a day, but 

 when put from sea water directly into a 8/8 m or 

 9/8 m solution they can live indefinitely. It was found ' 

 that if the concentration of the sea water was raised 

 gradually (by m/8 a day) the fish on the fifth day could 

 resist a 10/8 m solution of NaCl+KCl + CaCl^ for a 

 month (or possibly indefinitely; the experiment was 

 discontinued after that period). When a 10/8 m solu- 

 tion was allowed to become more concentrated slowly 

 by evaporation (at room temperature) all the fish died 

 rapidly when the concentration was 12/8 m or even 

 below. In higher concentrations they can live only 

 a day or two. These experiments show that while the 



' Loeb, J., Biochem. Ztschr., 19 13, li"-. 39 1- 



