124 PERMEABILITY 



is a decrease in permeability. This primarj^ effect is usually followed in time 

 by a secondary increasing effect upon permeability. These results were found 

 when these cations were associated with univalent anions. When the anions 

 are of higher valence the initial decreasing effect upon permeability may be 

 diminished or entirely offset. 



Similar effects of univalent and bivalent cations on the permeability of 

 the cytoplasm of the epidermal cells of onion bulb scales to water are recorded 

 by de Haan (1935). 



Raber (1920), using the same method and type of material as Osterhout, 

 studied the effects upon permeability of a number of salts composed of the 

 same cation (Na+) but different anions. All of these salts were found to 

 result in an increase in permeability. When supplied in equimolar concen- 

 trations the order of the increasing effect of the anions upon permeability was: 

 citrate > PO4 > tartrate > SO4 ; and acetate > CI > NO3 > Br > I > 

 CNS. The influence of the four polyvalent anions in increasing permeability 

 was much more marked than the univalent anions. Both of these series fol- 

 low closely the lyotropic order as usually given for anions. 



The effect of any electrolyte upon permeability can be analyzed only in 

 terms of the anions and cations into which it dissociates. The results of con- 

 ductivity experiments seem to indicate that the following general principles 

 hold (Raber, 1923) : If the valency of the anion exceeds that of the cation, 

 the salt results in an increase in permeability. If the converse is true the 

 initial effect of the salt is a decrease in permeability; this is followed by a 

 secondary increasing effect. When cation and anion are of the same valence, 

 the effect will depend upon the relative size of the ions and other factors. 

 When both ions are univalent, however, the usual effect is an increase in 

 permeability. 



The interpretation of these effects of electrolytes upon permeability is 

 not entirely clear, but if we assume the cytoplasmic membrane to be com- 

 posed of negatively charged micelles, an explanation similar to that given in 

 the preceding chapter for the influence of ions upon imbibition would seem 

 to fit the facts closely. 



Not all studies of the effects of ions upon permeability have yielded results 

 in accord with those just discussed. For example Brooks (1927) found that 

 sodium, potassium, magnesium, and calcium chlorides in concentrations of 

 0.0125 to 0.05 molar all check the penetration of the dye "dahlia" into living 

 cells of Nitella. Similarly Iljin (1928) found that dilute solutions of the 

 above salts as well as several others all result in a decrease in the permeability 

 of the cytoplasmic membranes of the cells of various species to sugars. The 

 effects of electrolytes upon permeability of the cytoplasmic membranes prob- 



