CALVIN B. COULTER 



405 



A specific reaction in the immunological sense may be supposed to 

 take place between the sheep cells and the immune or native sensitizers 

 of rabbit or guinea pig serum. A reaction of the same nature can 

 hardly be thought of as occurring between sheep cells and their own 

 serum, and yet these sera act ahke as protective colloids to sheep 

 cells since in their presence agglutination of the cells is not observed 

 at pH 4.7; and further, they sensitize the cells to agglutination at the 

 characteristic reactions of the serum euglobulins. 



Pep 



cent 

 100 



pH 7.4 7.2 70 6.8 6.5 6.4 62 6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.5 4.4 



Fig. 1. Each curve represents a single experiment and gives as ordinates the 

 percentage of the total amount of complement added which has been absorbed 

 by sensitized cells at 4°C., with varying H ion concentrations as abscissae. 



If the cells from the tubes to which guinea pig serum has been added 

 be sedimented and reemulsified in isotonic saline solution, it is found 

 that they are not only perscnsitized, but within a certain range of re- 

 action have combined apparently with the end-piece fraction of com- 

 plement as well, since hemolysis occurs without further addition of 

 end-piece. This is shown in the experiments recorded in the curves 

 (Fig. 1). The phenomenon is obser\'ed regardless of whether the 



