CALVIN B. COULTER 409 



reaction within the cell of pH 6.8, which is the isoelectric point of 

 hemoglobin.^ 



With older cells the reaction within the cell may be at pH 6.8 when 

 that of the outside fluid is at the same point without the appearance of 

 a trace of agglutination. The phenomenon of agglutination appears 

 then to be related closely to an optimal reaction in the suspending 

 fluid and probably of the cell membrane and not to a definite reaction 

 in the interior of the cell. 



CONCLUSIONS. 



1. The addition of blood serum displaces the optimum for agglutina- 

 tion of red blood cells in a salt-free medium to the reaction character- 

 istic of flocculation of the serum euglobulin. 



2. This effect is not due merely to a mechanical entanglement of 

 the cells by the precipitating euglobulin, since at reactions at which 

 the latter is soluble it protects the cells from the agglutination which 

 occurs in its absence. 



3. A combination of some sort appears therefore to take place 

 between sheep cells and sheep, rabbit, and guinea pig serum euglobu- 

 lin, and involves a condensation of the serum protein upon the surface 

 of the red cell. 



4. At the optimal point for agglutination of persensitized cells 

 both mid- and end-piece of complement combine with the cells. 



5. Agglutination is closely related to an optimal H ion concentration 

 in the suspending fluid, and probably of the cell membrane, and not to 

 a definite reaction in the interior of the cell. 



* Michaelis, L., and Takahashi, O., Biochem. Z., 1910, xxix, 439. Michaelis, L., 

 and Davidsohn, H., Biochem. Z., 1912, xli, 102. Michaelis, L., and Airila, Y., 

 Biochem. Z., 1921, cxviii, 144. 



