CHAPTER XIX 



ELECTROKINETICS 



Bacteria, fern spores, and nearly all living cells, when freely 

 suspended in an aqueous medium, will migrate toward one pole or 

 the other when they are subjected to the influence of an electric 

 field. They must, therefore, possess an electric charge. If this 

 charge is characteristic of cells, it may possibly play a part in 

 their life and to some extent determine their activities. How far 

 this last statement is true cannot as yet be definitely stated. It 

 is, however, true that the electric charge on cells may be used to 

 determine other very fundamental qualities which are directly 

 responsible for the potentialities of cells and of organisms as a 

 whole. 



The electric charge on the surface of cells, and on nonliving 

 particles as well, is a colloidal property which is grouped with 

 others under the term electrokinetics. 



Classification. — The colloidal state of matter has many 

 physical properties peculiar to itself. Certain of these are 

 electrical and manifest themselves in the movement of particles, 

 or an aqueous medium, under the influence of an electric field. 

 If the ends of two wires coming from a source of current are put 

 into the colloidal dispersion of a metal or an oil or into a suspen- 

 sion of living cells such as bacteria, then the particles of metal, oil, 

 or bacteria will move toward one pole or the other. The move- 

 ment of colloidal particles in an electric field is known as cataphore- 

 sis, or electrophoresis. If, now, the particles are made to move 

 through the liquid by mechanical means, e.g., by allowing suf- 

 ficiently large ones to fall through a column of water, an electric 

 potential is produced. This phenomenon is known as the Dorn 

 effect. It is, in a sense, the reverse of cataphoresis in that in one 

 case mechanical motion is caused by an electric potential, while 

 in the other an electric potential is produced by mechanical 

 motion. 



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