TENSION PHENOMENA OF LIVING ELEMENTS. 135 



1. If a weak electric current is passed through water in which 

 an Amoeba is suspended, it is carried passively toward the anode, 

 indicating that it has a negative charge. This charge may be 

 due to confined anions. 



2. If a stronger electric current is passed through an Anm'ba, 

 it begins to disintegrate first at that surface nearest the anode. 

 The disintegration is probably due to the accumulation of ions 

 retarded l>y the plasma membrane. The ions in the medium are 



I- 1 pass around the Amoeba, but the contained ions must pass 

 i In- plasma membrane in order to migrate to the fleet rodes. 

 since tin- disintegration is toward the anode, it i- prol.ubly due 

 to anions which cannot get out of the Amoeba. Since no corre- 

 sponding disintegration begins toward the kathode, the plasma 

 membrane is probably more permeable to kations. 



Tin- Mir face tension of the Amoeba is very low, ami apparently 

 iiKT'M-i - on strong stimulation (indicated by rounding up <>I the 

 ii'<i). \Ve saw that stimulation in plant and muscle alls 

 caused increased permeability to ions, and consequently dis- 

 appear. mee of the normal electrical polarization, and thercbv 

 can-iir^. im r eased surface tension. \\'e might conclude therefore 

 that the low surface tension of the Amoeba is caused b\ electric 

 pulari/ation, due to the production of some metabolic elect rol. te 

 \\ho-e anions cannot escape; and that strong stimulation causes 

 increased permeability and hence disappearance of the electrical 

 polarization. 



This \\ould explain all negative tropisms of the Aniii:l><i. The 

 surface ten-ion of the portion most strongly stimulated is in- 

 . reased, an<l the Anucba Hows away from the stimulus. 



In order to explain positive tropisms we would have to make 

 another assumption. If the stimulus did not act directly on the 

 plaMiia membrane, but penetrated the Anuclm and acted on the 

 protoplasm, and increased the production of the metabolic 

 product producing polarization of the plaMiia membrane, it 

 would thereby decrease the surface tension. The local decrease 

 in MII lace tension would cause the Amoeba to tlou toward the 

 source of the stimulus, just as the quicksilver drop in dilute 

 ll\( ' Hows toward potassium bichromate in Bernstein's experi- 

 ment . 



