28 



ACTIONS OF DRUGS ON SURFACES 



these ultrafiltrates and the composition of the initial 

 solutions is due to the adsorption of ions at the surface 

 of the ovalbumin molecules. The crosses of Fig. 5 show 

 the results which would have been obtained if the excess 

 of ions at the surfaces of protein molecules had been 



Fig. 5. The adsorption of calcium ions upon ovalbumin molecules, p^ 

 is plotted horizontally, and the ratio: calcium in protein solution/ 

 calcium in ultra filtrate, vertically, o experimental values; X calculated 

 for electrostatic binding of calcium ; ® calculated for formation of cal- 

 cium-carboxyl complex with electrostatic binding 



produced by electrostatic factors only: clearly only part 

 of the effect can be attributed to electrostatic forces. The 

 open circles of Fig. 5 are calculated on the assumption 

 that the concentration of calcium at the surface of a pro- 

 tein molecule is raised by electrostatic interaction be- 

 tween the surface and the ions, and that the calcium ions 

 enter into an equilibrium of the following type with the 



