406 AGGLUTINATION OF RED BLOOD CELLS 



cells have first been sensitized with rabbit serum or not; in the latter 

 case the normal sensitizer of guinea pig serum, too small in amount 

 to be recognized by the usual means, is probably united with the cells. 

 In the experiments recorded cells were sensitized with approximately 

 8 units of sensitizer and added to tubes along with guinea pig serum 

 in such amounts as to give a concentration of one unit of complement. 

 n/10 NaOH and HCl were immediately added and the tubes kept 

 at 4°C. for 45 minutes. The cells were then sedimented, the super- 

 natant fluids pipetted off as completely as possible, and their pH 

 measured electrometrically. The cell sediment in each tube was 

 reemulsified in a constant amount of isotonic saline solution and the 

 tubes were incubated at 37°C. The curves show the percentage of 

 the total complement present which has been absorbed by or removed 

 along with the cells. This percentage was plotted from the titration 

 curve of the complement alone according to the method described 

 by Brooks^ and employed with slight modification^ by the author. 

 Five other experiments have given the same result; namely, that 

 at the point of optimal agglutination of the persensitized cells the 

 greatest amount of whole complement has been bound by the cells. 



Guggenheimer^ found that sensitized sheep cells in saccharose 

 solution carry down with them in sedimentation the mid-piece frac- 

 tion of guinea pig serum, and that the amount of mid-piece removed 

 increases with the degree of sensitization of the cells, so that a true 

 binding probably occurs. He could not detect, however, an absorp- 

 tion of the whole of complement by sensitized cells under these cir- 

 cumstances, even when the cells had been sensitized with 100 units. 

 In the experiments described above in which such an absorption ap- 

 pears to have taken place a small amount of end-piece must have 

 been present in the liquid phase of the sedimented cell mass, which 

 could not have been removed by washing without disturbing the 

 equilibrium relations between the cells and the sensitizer^ and com- 

 plement. According to the experience of Zinsser,^ the trace of end- 

 piece retained by the globuHn sediment in the partition of complement 

 by dialysis is sufficient to give complementary power to the globulin 



^ Brooks, S. C, /. Med. Research, 1919-20, xli, 399. 



" Zinnser, H., Infection and resistance, New York, 1914, 180. 



