32 THE NATURE OF LIFE 



from liquid to jelly or the reverse appar- 

 ently takes place with great ease and is a 

 characteristic feature of the creeping 

 movements. 



An eminent biologist of the last gener- 

 ation said that it would be futile to seek 

 for any simple explanation of the move- 

 ments of the ameba. You might as well 

 try, he said, to explain that the move- 

 ments of a gunny sack with a man in- 

 side are due to a very simple mechanism. 

 How far he was wrong may be judged 

 from the fact that it is now possible to 

 imitate the movements of an ameba to a 

 remarkable extent by means of simple 

 mixtures of oil and other substances. 

 Not only does a drop of this kind, which 

 we may call for convenience an artificial 

 ameba, creep about, but its interior, un- 

 der the proper conditions, shows cur- 

 rents and countercurrents. 



We cannot say that we have, as yet, a 

 complete explanation of ameboid motion 

 but we have gone far enough to make it 

 evident that mechanical factors are ade- 



