162 THE UNIQUENESS OF LIFE 



is in part determined by the past its own experience and 

 the history of its race. In the organism, as Bergson says, 

 the past is prolonged into the present. "Living things 

 therefore require an historical explanation. Non-living 

 things, on the contrary, have no history in the biological 

 sense of the word, and no inorganic thing carries its past 

 about with it" (Russell, 1911, p. 338). We have to pass, 

 therefore, to a new level of explanation, and whenever we 

 mention that the eel is one of a deep-sea race which has 

 adventurously taken to colonising the fresh waters just as 

 the salmon is one of a fresh-water race which has taken to 

 exploiting the resources of the sea, and notice further that 

 many animals return to their birth-place to breed, and that 

 some go back to their birth-place to die, a biological light 

 begins to be shed on the eel's strange story. And we have 

 but begun. Of course if the objector is prepared to main- 

 tain that the enregistering of experience by organisms is 

 nothing more than a special case of the peculiar way in which 

 colloids are influenced by their history, we can only say that 

 this theory must get more facts to back it before we can take 

 it very seriously. 



No one wishes to slacken investigation into the physiology 

 of migration a most fascinating and suggestive inquiry. 

 It is known that when eels become mature there is an altera- 

 tion in the metabolism, and that the altered metabolism af- 

 fects the carbon dioxide content of the blood, that this in- 

 creases irritability, and that this increases range and vigour 

 of movements, and, moreover, that changes in the metabolism 

 of the animal affect its reactions to chemicals in the water, 

 to gravity, and to currents. Much knowledge of this kind is 

 accumulating, but it seems to many that it does not grip the 

 problem unless it be taken along with the concept of the 



