632 THE WONDER OF LIFE 



Theory of Life make of a story like this ? What can the 

 physiology that is only applied physics and chemistry tell 

 us ? It can tell us, for instance, a most useful thing to know, 

 how the energy for the journey is obtained from chemical 

 explosions of oxidizable material in the muscles of the eel's 

 body. It can tell us some of the steps in the making of this 

 fuel out of the eel's food. It can tell us that the muscles 

 are kept rhythmically contracting by nervous stimuli ; 

 that the advent of sex-maturity often alters an animal's 

 reactions to external stimuli ; and so on for a whole volume. 

 It is all interesting and indispensable, but it does not really 

 help us much in trying to understand the migration of the 

 eels to the distant spawning grounds. Even if an omnis- 

 cient chemist and physicist could give an account in his 

 own language of all the physical and chemical happenings 

 that occur in the eel's body from the time it left the pond 

 to the day of its death, that would not make more intelli- 

 gible to the biologist the concatenation of all these into the 

 unified adventure of migration. 



' To the chemist ', Eussell says, ' confronted with this 

 problem, there is no fact of migration at all ; there is only 

 an intricate enravehnent of chemical reaction. To the 

 biologist the fact of migration to a particular region for a 

 particular purpose is cardinal '. 



If it be said that one can picture, in dreams at least, a 

 torpedo so delicately adjusted, that it descended rivers, 

 went out to sea, kept ofE the rocks, turned corners, and did 

 not explode until it could do so effectively in an area of 

 appropriate stimulation, the answer must be that this 

 mechanism is still a very hypothetical construction, and 

 that if it were constructed it would not be a fair sample of 



