2O4 RALPH S. LILLIE. 



It can be shown by an application of the Lippmann-Helmholtz 

 theory, connecting variations of surface-tension with changes in 

 the potential difference at the boundary surface between two 

 phases, 1 that increase in the ionic permeability of the plasma- 

 membrane must result in an increase in the surface-tension of the 

 cell. The original theory of Helmholtz 2 that the tension be- 

 tween (e. ".) mercury and the adjoining solution is maximal with 

 zero potential difference, and diminishes as the potential differ- 

 ence between the phases increases in consequence of the static 

 charge effects at the boundary has required modification of 

 recent years, since the specific effect of the ions at the boundary 

 appears, apart from the potential difference, to modify the surface- 

 tension. 3 Gouy's 4 extensive studies have shown that various sub- 

 stances, including many non-electrolytes, may modify the surface- 

 tension of mercury. The observed surface-tension in any special 

 case is thus dependent on (i ) the specific nature of the adjoining 

 surfaces ; (2) the presence of foreign substances at the boundary, 

 and (3) the potential difference across the boundary. In view of 

 the sharply defined discontinuity between (e. g.} an egg-cell and 

 its medium the two may be regarded as separate phases, 5 and the 

 tension of the cell surface may be justifiably regarded as subject 

 to the same laws as that of the mercury surface. The nature of 

 the substances at the boundary surface and the potential differ- 

 ence across, this surface are thus the factors to be considered. 

 Although both are imperfectly known, certain facts seem well 

 established. The surface film of cells contains fatty substances 

 and proteins, both of which have marked effects in lowering the 

 surface-tension of water ; they will thus, in accordance with 

 Gibbs' principle, tend to collect at the boundary, and the charac- 

 teristics of the plasma-membrane are no doubt largely due to this 



1 Lippmann, " Relations entre les phenomenes electriques et capillaires," Annales 

 de chimie et de physique, 5me Serie, T. 5, 1875, P- 494- 



2 Helmholtz, " Gesammelte Abhandlungen," Bd. I., 1882, p. 925. 



3 Cf. S. W. J. Smith, Philosophical Transactions, Series A, igco, 193, p. 47. 

 Also the papers of Warburg, G. Meyer, and Paschen. 



4 Gouy, Annales de chimie el de physique (7), vol. 29, p. 145 ; (S), vol. 8, p. 291, 

 and vol. 9, p. 75. 



5 The criterion for regarding two contiguous systems as distinct phases is essentially 

 that they shall be bounded by a definite surface of discontinuity exhibiting character- 

 istic energy relations (surface tension, etc. ). 



