PROTOPLASMIC STRUCTURE 121 



pensation dialysis" that the salts in serum (containing 

 10 per cent protein) are freely dialyzable. Pauli and 

 Samec have also shown that alkali salts are not more 

 soluble in serum than in water.^ 



There is the possibility of the formation of com- 

 binations with the amino-acids present in the proteins; 

 but the salts of such weak acids would theoretically be 

 almost completely hydrolyzed; i.e., a stable combination 

 with protein in which the salt is completely and firmly 

 bound is scarcely conceivable. Any protein-salt com- 

 binations thus formed would hydrolyze, and the products 

 of hydrolysis would diffuse out through the membrane if 

 the latter were permeable; and further hydrolysis would 

 proceed until an equilibrium was reached in which a 

 large proportion of salt was present in the free dissolved 

 state."^ 



General chemical theory thus indicates that only a 

 very small proportion of the salt in the cell can be in a 

 state of permanent combination with protein; hence the 

 characteristic difference between the salt-content of the 

 cells and that of the medium cannot be thus explained. 

 It is probable, therefore, that the semi-permeability of 

 the plasma membrane is an essential factor in making 

 possible this difference. 



If it were possible to measure the electrical con- 

 ductivity of the cell interior apart from that of the 

 plasma membrane, the question could be answered at 

 once. According to the view presented above, the chief 



* Pauli and Samec, Biochem. Zeitschrift, XVII (1909), 235. 



2 In other words, the proteins and other compounds present in the 

 cell could not hold more than a very small proportion of the salts in a 

 combined and indiffusible form. 



