214 IMMUNOLOGY 



In 1921 Coulter showed that the most favorable pH for the 

 clumping of unsensitized red cells is 4.75 and that this shifts to 

 5.3 when agglutinin is adsorbed by them. Since this latter is the 

 isoelectric point for serum globulin and since agglutinins like all 

 antibodies are precipitated out with the serum globulins, it sug- 

 gests that the red cells are filmed or coated with antibody globulin 

 when they adsorb agglutinin as illustrated in Figs. 10 and 11. 



LoEB (1923). — As further evidence lending support to the con- 

 ception that globulin is adsorbed by the red cells is the result of 

 Loeb's (1923) studies on the ability of collodion particles to ad- 

 sorb protein. He shows after adsorption of a film or partial film 

 of protein the collodion particles acquire the properties of the 

 adsorbed substance. According to Northrop (1928) this phenome- 

 non had been observed first by INIeyers and Lottermoser in 1901. 



Northrop and DeKruif (1922).- — Almost simultaneously with 

 the appearance of Coulter '.s work, Northrop and DeKruif (1922, 

 1923) published the results of their careful investigation of the 

 mechanism of agglutination. They studied tlie effect of pH on the 

 specific adsorption of antibody globulin Avhich corresponds to 

 Bordet's phase one and found that it does not seem to affect it ma- 

 terially since the adsorption of antibody globulin occurs through- 

 out a fairly wide range of pH values and even when both elements 

 are similarly charged. 



Shiblfa's Summary of Northrop and DeKruif 's Work. — Their 

 final conclusions including the results of their studies on phase two 

 of Bordet are concisely summarized by Shibley* (1926) as follows: 



''(1) Agglutination is to be considered in terms of two antago- 

 nistic forces ; a repelling force, due to like electrical charges, which 

 tends to keep the bacteria apart, and 'cohesive force,' wliicli 

 makes for adhesion. In any bacterial sus]>ension, all factors that 

 make the repelling force relatively greater than the cohesive force 

 make for stability; and conversely, all factors tliat reduce the re-, 

 pelling force or otherwise make the cohesive force relatively 

 greater, lead to flocculation. (2) In the case of unsensitized 

 bacteria, electrolytes in lower concentrations, < 0.01 N, affect 

 primarilj^ the potential, and in higher concentrations, > 0.01 - 

 0.1 N, affect primarily the cohesive force. (3) As long as the 



•Shibley: J. Exper. Med. 44: 667, 1926. 



