THE ISOELECTRIC POINT OF RED BLOOD CELLS AND ITS 

 RELATION TO AGGLUTINATION. 



By CALVIN B. COULTER.* 



{From the Hoagland Laboratory, Brooklyn.) 



(Received for publication, October 21, 1920.) 

 INTRODUCTION. 



A number of investigations have been made into the electrical 

 charges carried by bacteria and other cells in watery suspension. 

 The movement observed in cataphoresis is affected by a number of 

 factors, the analysis of which is so difiEicult that we have at the present 

 time very little information as to the relation between agglutination 

 and the electrical charge of the cells. Cellular suspensions behave in 

 many ways like colloidal solutions, and it is generally understood now 

 that colloidal protein solutions are amphoteric electrolytes. Their 

 colloidal particles carry a negative charge in alkaline reactions and a 

 positive charge in acid reactions; at a definite hydrogen ion concen- 

 tration there exists no difference in electrical potential between the 

 particles and the medium, so that the particles appear uncharged. 

 This is known as the isoelectric point. At this point a number of 

 physical properties such as solubility, viscosity, and conductivity pass 

 through a minimum. Further, as shown by Loeb,^ the isoelectric 

 point is a turning point for the chemical change that determines the 

 nature of the ionization. It is to this ionization that the electrical 

 charge is due, so that when ionized as an acid and combined with the 

 cation on the alkaline side of the isoelectric point the protein particle 

 behaves as an anion and moves in the electric field to the anode; 

 when ionized as a base and combined with anion, at reactions more 

 acid than the isoelectric point, the protein becomes part of a complex 



* Van Cott Fellow in Pathology. 



^ Loeb, J., /. Gen. Physiol, 1918-19, i, 39, 237, 363, 483, 559. 



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