IV] STRUCTURE OF THE CELL 187 



only in so far as they are inseparable from the problems presented 

 by the visible configurations of form and structure, and while we 

 try, as far as possible, to evade the difficult question of what 

 particular forces are at work when the mere visible forms produced 

 are such as to leave this an open question, yet in this particular 

 case we have been drawn into the use of electrical analogies, and 

 we are bound to justify, if possible, our resort to this particular 

 mode of physical action. There is an important paper by R. S. Lillie, 

 on the "Electrical Convection of certain Free Cells and Nuclei*," 

 which, while I cannot quote it in direct support of the suggestions 

 which I have made, yet gives just the evidence we need in order 

 to shew that electrical forces act upon the constituents of the 

 cell, and that their action discriminates between the two species 

 of colloids represented by the cytoplasm and the nuclear chromatin. 

 And the difference is such that, in the presence of an electrical 

 current, the cell substance and the nuclei (including sperm-cells) 

 tend to migrate, the former on the whole with the positive, the 

 latter with the negative stream : a difference of electrical potential 

 being thus indicated between the particle and the surrounding 

 medium, just as in the case of minute suspended particles of various 

 kinds in various feebly conducting media "j". And the electrical 

 difference is doubtless greatest, in the case of the cell constituents, 

 just at the period of mitosis : when the chromatin is invariably 

 in its most deeply staining, most strongly acid, and therefore, 

 presumably, in its most electrically negative phase. In short, 



* Amer. J. of Physiol, via, pp. 273-283, 1903 [vide, supra, p. 181); cf. ibid. 

 XV, pp. 46-84, 1905. Cf. also Biological Btilleti^i, iv, p. 175, 1903. 



f In Uke manner Hardy has shewn that colloid particles migrate with the 

 negative stream if the reaction of the surrounding fluid be alkahne, and vice versa. 

 The whole subject is much wider than these brief allusions suggest, and is essentially 

 part of Quincke's theory of Electrical Diffusion or Endosmosis: according to 

 which the particles and the fluid in which they float (or the fluid and the capillary 

 walls through which it flows) each carry a charge, there being a discontinuity of 

 potential at the surface of contact, and hence a field of force leading to powerful 

 tangential or shearing stresses, communicating to the particles a velocity which 

 varies with the density per unit area of the surface charge. See W. B. Hardy's 

 paper on Coagulation by Electricity, Journ. of Physiol. xxn% p. 288-304, 1899, 

 also Hardy and H. W. Harvey, Surface Electric Charges of Living Cells, Proc. R. S. 

 Lxxxiv (B), pp. 217-226, 1911, and papers quoted therein. Cf. also E. N. Harvey's 

 observations on the convection of unicellular organisms in an electric field (Studies 

 on the PermeabiHty of Cells, Journ. of Exper. Zool. x, pp. 508-556, 1911). 



