INORGANIC SALTS 179 



of the protoplasmic surface-film, on this hypothesis, is 

 evident. 



The possibility of a reversibility of phase-relations 

 under salt action^ implies the possibility of inducing 

 reversible changes of permeability under these conditions, 

 and such reversible changes are, as we have seen, a 

 characteristic feature of the living plasma membranes. 

 Clowes has in fact constructed a model in which an 

 emulsion consisting of equal volumes of oil and a mixed 

 salt solution (containing NaCl, KCl, and CaCla in propor- 

 tions similar to those of sea water and slightly alkaline) 

 is supported in the interstices of a paper partition (sheets 

 of filter paper) fixed in position by rings of rubber in the 

 interior of a U-tube.^ The electrical conductivity of 

 the emulsion-permeated paper is then found to vary, 

 when the solution in contact with it is changed, in a 

 manner resembling in general that shown by the parti- 

 tion of living plant-tissue in Osterhout's experiments. 

 In pure NaCl solution the conductivity is rapidly 

 increased; in pure CaCla it is decreased; and the changes 

 of conductivity are reversible if they are not allowed to 

 proceed too far. It is assumed that in the capillary 

 interstices the emulsion undergoes reversible changes of 

 phase of the above-described kind, the conversion of the 



* For the conditions of the reversibility of .phase-relations in emul- 

 sions cf. Newman, Journal of Physical Chemistry, XVIII (19 14), 34; 

 Briggs and Schmidt, ihid., XIX (1915), 478; Clowes, ihid., XX (1916), 

 407; Bhatnagar, Jour. Chem. Soc. Trans., CXVII (1920), 542; also 

 Physics and Chemistry of Colloids, Discussion of Faraday Society and 

 Physical Society of London (1921), p. 27; also in Kolloid-Z., XXVIII 

 (1921), 206. 



' Clowes, Proceedings of the Society of Experimental Biology and 

 Medicine, XV (1918), 108. 



