INORGANIC SALTS 175 



isotonic NaCl solutions, while none revive in supar 

 solution. A ''salt action " is necessary to the penetration 

 of KCl in either direction through the membrane; all 

 salts, however, are not equally effective; in the case of 

 Na salts the effect shows an increase with increase in 

 the valence of the anion. These effects apparently 

 indicate that the penetration of ions through a membrane 

 consisting of colloidal material with which the ions 

 form compounds (proteinates) requires the presence of 

 other free ions with which the penetrating ion can form 

 alternative combinations. Otherwise it is held in 

 position by chemical forces and unable to move freely. 

 Similar conditions have been observed in the diffusion 

 of dyes (neutral red) from stained eggs; this diffusion is 

 also facihtated by the presence of salts in the outer 

 medium. In order to obtain the maximum diffusion- 

 facilitating salt-effect a certain medium concentration 

 of the effective salt is required; higher concentrations 

 and lower concentrations have a retarding influence on 

 diffusion; this latter effect appears to form the basis 

 of the usual salt-antagonisms or protective effects shown 

 by calcium and other bivalent salts. ^ 



It is evident that changes in the physical properties 

 of membranes must alter the readiness with which diffus- 

 ing materials penetrate, and that such changes may result 

 from changes in the chemical composition of the 

 membrane-forming compounds as well as from changes in 

 their distribution or state of subdivision. In a membrane 

 consisting of protein, the formation of proteinates with 

 varying physical properties will change the permeability 

 and the other properties of the membrane. Similarly 



^Loeb, Journal of Biological Chemistry (1916), loc. cit. 



