300 PROTOPLASM 



chemical changes at the anterior end of the body of an 

 Amoeba, extension-currents must necessarily arise, as I have 

 pointed out already, at the surface of the body of an 

 Amoeba, in connection with these changes. Hence, if 

 Berthold denies generally the existence of any currents in 

 the water surrounding an Amoeba, this is, in my opinion, just 

 as strong evidence against his own theory as against the one 

 brought forward here. I hardly think he could be of opinion 

 that the chemical changes in the protoplasm only extend to 

 the under side of an Amoeba, i.e. to its adherent surface, 

 since he regards the entire hyaline protoplasm of the 

 anterior end as that which is chemically changed. In any 

 case, however, this change must extend to the edge of the 

 adhering surface, and here come into contact with the sur- 

 rounding medium, so that differences of surface-tension 

 would necessarily exist in this region, and cause currents to 

 be set up. But, as I have already explained in discussing 

 the drops that retreat from alcohol, I consider it as on the 

 whole impossible that forward movements can be brought 

 about by such a change in the adhesion without accom- 

 panying differences of tension in the free surface of the 

 drop. On the contrary, such a change would only give rise 

 to a single alteration in the shape of the drop. 



On the ground of the foregoing explanations, therefore, 

 I must regard Berthold's explanation of amoeboid movement 

 as unsuitable, at least in so far as it has been possible for 

 me to rightly understand his train of argument. 



It seemed to me, however, of interest to test more 

 accurately, by means of experiment, the relations of the 

 system of currents in the drops of water, which are 

 theoretically postulated as necessary during their retreating 

 movements. It was thereby proved, after some unsuccess- 

 ful experiments, that the phenomena take in the main just 

 the course that was assumed above. In order to convince 

 oneself of this fact, it is best to proceed by placing drops of 

 water on a glass plate cleaned as well as possible, and then 

 causing a capillary tube, of not too great fineness, or a glass 

 r"od, with ether, to approach their margin. If some ivory 

 black has been mixed with the drops, it can be observed 



