412 WILLIAM A. KEENER AND WILLIAM H. TALIAFERRO. 



the Amceba resides a 'Miniaturpsyche' an energy absent in the 

 inorganic." Thus the simplest phenomenon of life in one of 

 the simplest animals has not been reduced to terms of physics 

 and chemistry. 



Despite this fact there is much, as yet, said concerning the 

 physical and chemical explanation of the food-reactions of 

 Amceba. For instance Hegner ('10) says in speaking of the food 

 reaction of Amoeba that "this apparent choice of food may be 

 due to ordinary physical laws of fluids." Likewise Calkins 

 ('09) says: "While most of the actions of protozoa are reactions 

 to external stimuli, many are combinations of reactions which 

 do not lend themselves to analysis. Such, for example, is the 

 apparent choice of food or of building material for shells and 

 tests, or the complex reactions that are frequently involved in 

 the avoidance of some obstruction. Many of these so-called 

 conscious acts can be explained by the ordinary physical laws 

 of fluids." 



At a more recent date McClendon ('12) showed that by a 

 disturbance of the electrical polarization the surface tension 

 would be modified and adds: "We might conclude therefore that 

 the low surface tension of the Amceba is caused by electric 

 polarization, due to the production of some metabolic electrolyte 

 whose anions cannot escape; and that strong stimulation causes 

 increased permeability and hence disappearance of the electrical 

 polarization. 



' This would explain all negative tropisms of the Amceba. The 

 surface tension of the portion most strongly stimulated is in- 

 creased, and the Amceba flows away from the stimulus. 



"In order to explain positive tropisms we would have to make 

 another assumption. If the stimulus did not react directly on 

 the plasma membrane, but penetrated the Amceba and acted on 

 the protoplasm, and increased the production of the metabolic 

 product producing polarization of the plasma membrane, it would 

 thereby decrease the surface tension. The local decrease in 

 surface tension would cause the Amceba to flow toward the 

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

 HNOs flows toward potassium bichromate in Bernstein's experi- 

 ment." 



