1911.] Note on Surface Electric Charges of Living Cells. 219 



current gave, for the layer next the glass, where they moved in opposite 

 directions, 079 division per second, and for the middle region, where they 

 moved in the same direction, - 81 division per second — an agreement within 

 the limits of error of observation. 



Electrification of its surface, due to contact with the medium in wnioh it 

 lives, must modify endosmotically the passage of substances into or out of a 

 living cell ; one might expect, therefore, that a part of the work of the cell 

 would be expended in controlling this polarisation. It is unfortunately 

 difficult to get reliable information on this point. 



The fact that yeast and blood corpuscles migrate to the anode in isotonic 

 sugar at different rates probably means that the negative charge per unit 

 area on the red corpuscle is greater than that on the yeast cell, for, 

 according to theory, the velocity, due to shedding of the charged fluid layer, 

 is independent of the size or shape of a particle, provided the slip at the 

 interface be small compared with the dimensions of the particle.* This last 

 condition is usually held to be fulfilled by solid particles of finite size, but it 

 must be remembered that the interface between the enormous molecules ot 

 living matter and a fluid possibly differs widely in its properties from that 

 between inert solid and fluid. Some features in the transport of fluid 

 through living membranes seem to point to a very high coefficient of slip. 



Another difficulty is that observation must be on cells in their natural 

 habitat. Yeast and blood corpuscles in isotonic sugar solution are not in an 

 indifferent medium, which leaves their properties unchanged. Isotonic sugar 

 solution washes electrolytes out of muscle fibres, for instance, and so induces 

 paralysis. The diffusion of salts out of yeast and blood corpuscles will 

 polarise the surface to an extent determined by the osmotic properties of 

 the surface and the nature of the salts. 



The effect of poisons may be explained in this way. Chloroform, toluene, 

 or traces of mercuric chloride reverse the sign of the charge on living cells, 

 a second reversal, that is a return to the original charge, occurring after two 

 or three days. The death change, however, is known to be accompanied by 

 the liberation of salts, which previously were not " free,"f and the change in 

 the polarisation of the surface may be referred to the diffusion of such salts 

 out of the cell. The electrification of the surface certainly does not depend 

 upon the intactness of the cell, for fragments of yeast cells broken up by 

 pounding in a mortar moved in the same way, and at much the same rate, 

 as did intact cells. 



* Lamb, 'Brit. Assoc. Report,' 1887, p. 501. 



t Macdonald, 'Boy. Soc. Proc.,' 1905, B, vol. 76, p. 322; Macallum, ibid., 1906, B, 

 vol. 77, p. 165. 



