217 



Note on the Surface Electric Charges of Living Cells. 

 By W. B. Hardy, F.E.S., and H. W. Harvey. 



(Eeceived June 21,— Read June 29, 1911.) 



The movement of free living cells suspended in a fluid through which an 

 electric current is passing towards one or other of the poles has been described 

 by many observers. In almost every case the movement has been observed 

 in thin films of fluid under a cover-glass mounted in the way usual for 

 microscopical examination. The cells do not always all move in the 

 same direction ; sodfe migrate towards the anode, others to the cathode, and 

 Thornton* found that in mixed suspensions of diatoms and amcebse, or yeast 

 cells and red blood corpuscles, the animal cells migrated to the anode, the 

 vegetable cells to the cathode. He infers from this that animal and vegetable 

 cells are oppositely electrified, the former being negative, the latter positive, to 

 the fluid. 



It is obvious at the outset that there are exceptions to this generalisation, 

 for Becholtf describes a movement of bacteria towards the anode, the direction 

 being reversed after agglutination. DaleJ and Lillie§ also have described 

 movements of animal cells to the cathode, but Thornton points out with some 

 justice that in these cases the cells were not in their normal habitat. 



The objection does not, however, apply to a natural culture of Gonium, 

 Vorticella, and Amoeba. In thin films such as Thornton used we found that 

 the first two moved towards the cathode, while the amoebae moved to the 

 anode. 



The movement of living cells, or indeed of any suspended particle, in films 

 of liquid a millimetre or less in depth enclosed between glass plates is not 

 open to the simple interpretation which Thornton places upon it. Arising 

 from a contact difference of potential at the glass-water interfaces the upper 

 and lower surface films of the water are dragged along in the electric field 

 with considerable velocity on account of the ions they contain, and the flow 

 along the boundary so produced is compensated under hydrostatic pressure 

 by a return flow in the middle or round the edges of the stratum of water, if 

 it be thick enough. The velocity of a particle past the observer is the sum of 

 the velocity of the fluid and the velocity of the particle through the fluid, and 



* 'Eoy. Soc. Proc.,' 1910, B, vol. 82, p. 638. 

 t ' Zeit. Phys. Cheni.,' 1904, vol. 48, p. 385. 

 % 1 Journ. of Physiol.,' vol. 26, p. 219. 

 § ' Anier. Journ. of Physiol.,' 1893, vol. 8, p. 273. 



