CALVIN B. COULTER 521 



CONCLUSIONS. 



1. In a salt-free medium the proportion of the total amount of 

 hemolytic sensitizer present, combined with the homologous cells, 

 reaches a maximum of almost 100 per cent at pH 5.3. On the alkaline 

 side of this point the proportion combined diminishes with the alka- 

 linity and reaches a minimum of approximately 5 per cent at pH 

 10. On the acid side of pH 5.3 the proportion combined diminishes 

 with the acidity but somewhat less rapidly than for a corresponding 

 increase in alkalinity. 



2. The presence of NaCl greatly increases the proportion of sensi- 

 tizer combined with cells at all reactions except those in the neighbor- 

 hood of pH 5.3. At this point the combination of sensitizer with 

 cells is independent of the presence of electrolyte. 



3. The curves representing the proportion of sensitizer combined 

 or free run almost exactly parallel, both when the sensitizer combines 

 de novo and when it dissociates from combination; therefore, in con- 

 stant volume, at a given hydrogen ion concentration, and at a given 

 temperature, an equilibrium exists between the amount of sensitizer 

 free and that combined with cells. 



4. The combination of sensitizer and cells is related fundamentally 

 to the isoelectric point of the sensitizer. 



5. The dissociated ions of the sensitizer, formed either by its acid 

 or its basic dissociation, do not unite with cells. Combination takes 

 place only between the cells and the undissociated molecules of the 

 sensitizer. 



