CALVIN B. COULTER 



517 



only electrolyte present was that added with the immune rabbit 

 serum. The mixture of cells and serum was left standing for 30 

 minutes in the water bath at 38°C. and 1 hour in the refrigerator at 

 about 8°C., then centrifugated, and the supernatant fluid drawn off. 

 The pH of this was usually about 6.5. The cells were then washed 

 once or twice in saccharose solution and made up to 10 per cent 

 strength. From this point the procedure was the same as for the 

 combination of sensitizer except that the addition of 0.1 cc. of sensi- 

 tizer was omitted. The supernatant fluids from the sensitization and 



Fig. 1. Curve showing the proportion of the total sensitizer present either free 

 or combined with cells, when the two combine de novo. 



from the washing of the sensitized cells were titrated for their content 

 of antibody and the sum of these values subtracted from the value 

 of the immune serum itself. The remainder gives the amount of 

 sensitizer actually in combination with the cells. 



The results of both series of experiments are given in the form of 

 curves, Fig. 1 for combination and Fig. 2 for dissociation. The 

 abscissas represent pH values, the ordinates the percentage of the 

 total amount of sensitizer present either free or combined with cells. 

 The curves show that near pH 5.3 the amount of sensitizer free in the 

 supernatant fluid is at a minimum and the amount combined with the 



