OF VITAL PHENOMENA 151 



The action of an electric field on an ameba on a substratum 

 is in 'harmony with this view. The anions within the ameba are 

 massed on the inside of the plasma membrane toward the anode 

 because they cannot pass through it. When they have accumu- 

 lated to a sufficient concentration they act as a stimulus, increasing 

 its permeability, and the ameba moves toward the cathode. This 

 is not due to electric convection, since a suspended ameba is 

 carried toward the anode by this means, electric convection being 

 anodic whereas galvanotropism is cathodic. 



We may explain the irregular movements of the ameba when 

 not under a single directive stimulus as due to varying and local- 

 ized influences of the environment on its permeability, or to 

 localized variations in its metabolism, resulting in variations in 

 the production and concentration of the electrolyte responsible 

 for the electrical polarization. 



Certain substances dissolved in the medium increase and others 

 decrease ameboid movements although the mechanism of their 

 action is not known. Hamburger (1912) observed that anes- 

 thetics in certain low concentrations increase the ameboid motion 

 of leucocytes. He found that a saturated solution of iodoform 

 had the right concentration, and hence its efficacy in salves in 

 increasing phagocytosis. This explanation rests on the assump- 

 tion that the phagocytic action of the leucocytes varies with their 

 ameboid activity. Substances which increase their phagocytic 

 action were called opsonins by Wright, but whether such sub- 

 stances have their primary effect on the leucocytes or the bacteria 

 seems undecided. 



Ross (1911) claims that alkaloids increase ameboid move- 

 ments. 



The idea that gelation and solation, and swelling and shrinking 

 of gels are factors in ameboid movements was first expressed by 

 Montgomery (1878, 1881), being more recently advanced by 

 Rhumbler and others. 



The contractile vacuole seems to be an organ of defense of 

 the ameba against the swelling action of the hypotonic medium. 

 Hal-tog has shown that it is universal among fresh water amebas 

 but may be absent in parasitic and marine forms. It may be 

 remarked, however, that even some phagocytes in exudates have 

 contractile vacuoles. 



