640 



R. J. GOLDACRE 



is probably an electrical phenomenon of some kind. If you reverse the electric 

 charge by pre-treating them with polyethylene imine solution, they move in the 

 opposite direction and form a clump on the amoeba's tail. 



Another experiment which shows that the membrane does not move forwards 

 is as follows : if you put an amoeba into a narrow capillary tube so that it is squeezed 

 on all sides, becoming thereby about twice its natural length, it continues to crawl 

 through the tube. If the membrane was moving forwards this would not happen. 

 Also, if you put parallel glass fibres on the surface of the amoeba with a micro- 

 manipulator, so that one end rests on the amoeba and the other on the slide (see 

 Fig. Ai), then as the amoeba moves forwards those in the rear are pulled together 

 whereas those in the front remain unmoved. Contraction therefore appears to occur 

 in the tail region, with the membrane remaining stationary in the middle portion 

 of the amoeba, and forming de novo in the front. 



1. 



'tii) 



Allen: In the next issue of Experimental Cell Research Dr. J. L. Griffin and I 

 are publishing pictures of a monopodial amoeba which is turning to the left. A 

 carbon particle attached to the left side advances toward the front of the cell, over 

 the hyaline cap and comes to lie on the right side of the pseudopod. I think this 

 experiment very nicely invalidates the idea that a bioelectric phenomenon might 

 be the cause of forward movement of particles attached to the plasmalemma. 

 While an amoeba can form a new membrane (e.g. to replace that lost during phago- 

 cytosis), all available evidence suggests that there is not much membrane turnover 

 during active locomotion. 



Porter: I understood that you take the foldings in the tonoplast membrane 

 or the vacuolar membrane to be indicative of contraction, is that so ? Could those 

 not also represent a production of excessive membrane at 8 sites on the surface of 

 the tonoplast ? 



GoLDACRE : Perhaps, but since the motion is towards the site of the deeper 

 region of cytoplasm you would expect that the surface membrane would inevitably 



