OSTERHOUT— DYNAMICAL THEORY OF ANTAGONISM. 541 



To this however there is the objection that the maximum 

 amount of Na„oZCaCl22 which is produced in NaCl 95.24 -{- CaCL 

 4.76 could also be obtained in other mixtures, e. g., in NaCl 50 -|- 

 CaCU 50 if the total concentration of salts in the latter mixture 

 were increased to the requisite amount. This is contrary to what 

 we find in antagonism experiments. If antagonism really depends 

 on the production of a salt compound like Na^oXCaCUo it is evident 

 that some mechanism must exist which insures that an increase in 

 the total concentration of salts can have but little effect as compared 

 with that produced by a change in their relative proportions. 



It is easy to see how such a mechanism must exist if the forma- 

 tion of Naoo-^CaCloo takes place at a surface (at the external surface 

 of the cell or at internal surfaces). In a surface substances usually 

 exist in a dififerent concentration from that which they have else- 

 where in the solution. If NaCl and CaCU migrate into the surface, 

 so as to become more concentrated there than in the rest of the 

 solution, their concentration in the surface must increase as their 

 concentration in the solution increases until a certain point (called 

 the saturation point) is reached. Beyond this point an increase in 

 their concentration in the solution produces no effect on their con- 

 centration in the surface. 



When this stage has been reached the formation of Naoo^CaCLo, 

 if it takes place in the surface, will not be affected by an increase in 

 the concentration of the salts in the solution. It will, however, be 

 affected by changes in the relative proportions of the salts. The 

 number of molecules of salt in a unit of surface will remain nearly 

 constant, but if the proportion of NaCl in the solution be increased 

 some of the CaCL in the surface will be displaced by NaCl. 



Below the saturation point the relative proportions of the salts 

 will be of less importance than their total concentration : this is the 

 case at low concentrations in the region of the so-called " nutritive 

 effects." 



It may be added that these considerations apply no matter 

 whether the salts which migrate into the surface come from the 

 outside or from within (or from both directions) : also that they 

 apply when the surface is completely permeable to salts (so that 

 we do not assume an impermeable surface in order to account for 



