298 PROTOPLASM 



low surface tension, which was brought into contact on one 

 side with water or another iiuid of higher surface tension ; 

 since water is less volatile than alcohol, the experiment 

 could not be carried out in the same manner as the reverse 

 one. E"ow, if the adhesion was increased, or, in other 

 words, the surface tension of the drop towards the glass was 

 diminished, by the surface of the drop of alcohol taking up 

 water on one side, so that this edge of the drop spread itself 

 out with diminution of the marginal angle, then, by reason 

 of the difference of tension on the free surface of the drop, 

 which would necessarily result, a superficial extension- 

 current would at once arise, whose centre of course 

 would be situated at the opposite edge of the drop. If 

 this current was continuous, as would of course be the 

 case if the polar difference of the surface tensions in the 

 drop was maintained — that is to say, if water was more 

 volatile than alcohol, — a movement forwards of the drop 

 towards the side of the water would be the natural con- 

 sequence. 



From these reflections it seems to me obvious that, if 

 amcfiboid movement had as its cause what Berthold ascribes 

 to it, a system of currents ought to be set up in an Amoeba 

 exactly the reverse of what actually exists. The currents 

 should flow away from the hinder end of an Amoeba on 

 each side and carry protoplasm to the anterior end. But 

 since it is notorious that the streaming takes exactly the 

 opposite course, I consider Berthold's hypothesis unsuitable. 

 Now, Berthold has well remarked that the currents in an 

 Amceba run, in the main, just as if an extension-current 

 existed as the result of the surface tension being diminished 

 at the anterior end, as is the case in our drops of oil or oil- 

 foam. Nevertheless, he considers it incorrect to accept this 

 obvious hypothesis as a means of explaining amoeboid move- 

 ment. He is more inclined to think that the successive 

 spreading out of protoplasm at the anterior end of an 

 Amoeba takes place with considerable force, and that 

 thereby not only the axial up current, but also the back 

 currents on each side, are to be explained. In opposition 

 to this idea I must point out that it seems to me quite 



