1911..] Note on Surface Electric Charges of Living Cells. 221 



were) by the skin through the tube."* At the free surface of a fluid, 

 therefore, there must be relatively! enormous forces dragging the surface 

 skin and the water in opposite directions if the movement of the water be 

 due to a difference of potential between it and a surface film of impurities 

 condensed from the air or neighbouring solids. The only escape from this 

 conclusion is that the movement of the water is due to a circulation pro- 

 duced by the endosmotic movement of the layer touching the glass, but 

 any compensating circulation would be opposed in direction to the flow at 

 the glass face, whereas the surface flow is in the same direction — it is, in 

 fact, precisely what it would be if the air and surface film were replaced by 

 a plate of glass. 



It seems difficult to avoid the conclusion that the film acts in the electric 

 endosmose as though it were a rigid solid, and its properties are the same, 

 when all ordinary precautions are taken to avoid contaminating the surface, 

 as when a very thin layer of oil is allowed to spread over the water. 



If the surface film really acts, as it would seem to, as a fixed layer past 

 which the water is driven, since the stresses would be purely tangential, 

 it is only necessary to regard it as having tenacity and as being anchored 

 all round to the unwetted glass walls, and the apparent tenacity of the 

 film will be partly true tenacity due to the forces between its component 

 molecules and partly due to the work needed to rupture the film and expose 

 a fresh water-air interface. 



When the floating particles move at all, the movements are slight, irregular 

 in direction (that is to say, they may be at an angle to the stream lines), 

 and the direction is not reversed when the current is reversed. When the 

 electrodes are placed directly in the distilled water, so as to cut out the 

 large resistance of the end plates of porous earthenware, and the current 

 thereby increased to O01 ampere or more, these movements are more rapid, 

 and the submerged particles also now move in the same general direction 

 as the floating particles, and their movement ceases to reverse when the 

 electric field is reversed. 



These movements, at first sight puzzling, admit of a very simple explana- 

 tion. In the first place the direction is determined by the trough used and 

 not by the current. That is to say, if the particles move from right to left 

 no matter how the current is running, and the trough is displaced end for 

 end, they now move from left to right. If we regard the gain of heat per 

 unit of time from the current as being symmetrical with respect to the 



* H. Lamb, loc. cit. 



t Kelative, that is, to the surface stresses in ordinary flowing due to differences of 

 hydrostatic pressure. 



