lyo PROTOPLASMIC ACTION AND NERVOUS ACTION 



The evidence, taken as a whole, indicates that the 

 salts act chiefly by altering the physical state of the 

 structural colloids of the cell; and it is to be presumed 

 that general physical factors (of the kind regarded as 

 acting in all colloidal phenomena) and special chemical 

 factors specific for each form of protoplasm are both 

 concerned in producing the total effect. In the directly 

 toxic or injurious action of salt solutions, a frequent, if 

 not invariable, factor is a destruction of the semi- 

 permeable properties of the protoplasmic partitions, 

 primarily of the plasma membranes. In physiological 

 salt-actions of other kinds, e.g., stimulation, sensitization, 

 inhibition, it is to be presumed that the physical proper- 

 ties of the plasma membranes undergo special modifica- 

 tions of a corresponding kind, but that the effects do not 

 exceed a certain range and are therefore reversible. 

 The general fact that a certain combination of salts, 

 usually of Na, Ca, and K, is required in the external 

 medium for most forms of normal protoplasmic action 

 indicates the fundamental importance of the influence 

 of salts on the structural colloids of protoplasm. Appar- 

 ently the structural conditions required for the continuity 

 and closeness of texture necessary in semi-permeable 

 membranes depend on the maintenance of a definite 

 equihbrium between the ions in the medium and those 

 associated (chemicaUy or otherwise) with the structural 

 coUoids. SKght changes in the salt-content imply 

 corresponding structural changes, with dependent physio- 

 logical effects. 



It should be added that other general physical 

 conditions, also dependent on the presence of salts, 

 are of importance in the normal activity of protoplasm, 



