404 AGGLUTINATION OF RED BLOOD CELLS 



The euglobulin precipitates most promptly and completely from 

 rabbit serum diluted 1:20 with distilled water at the same reaction, 

 pH 5.5, and it is apparent that the agglutination of the cells is inti- 

 mately related to the precipitation of the serum euglobulin. 



The same relation is observed in the agglutination of sheep cells to 

 which a like small amount of their own active seriun has been added, 

 as shown by the following values for the optimal point for agglutina- 

 tion in the presence of homologous serum: pH 5.58, 5.44, and 5.38. 

 The euglobulin itself precipitates best from sheep serum diluted 

 1 : 20 with distilled water at approximately pH 5.5. 



Guggenheimer^ has made an observation which corresponds closely 

 with this, that if defibrinated sheep blood be washed directly with 

 isotonic saccharose solution the euglobuHn of the serum is carried down 

 with the cells and will serve as the mid-piece fraction of complement to 

 persensitize the cells on the subsequent addition of sensitizer. 



The relation mentioned is noted again when sensitized sheep cells 

 in saccharose solution are persensitized by the addition of active 

 normal guinea pig serum. If such serum be added in the amount of 

 8 per cent of the total volume to an emulsion of sensitized cells of such 

 concentration that one unit of complement is present, the optimal 

 point for agglutination has been found at the following electrometric 

 values: pH 6.19, 6.35, and 6.15. Five other experiments in which 

 the estimation was made colorimetrically gave values between pH 

 5.9 and 6.3. The euglobuHn has been found to precipitate best from 

 guinea pig serum diluted 1 : 20 with distilled water between pH 6.2 

 and 6.4 (electrometric).^ 



If the cells were persensitized at pH 6.2 and washed by allowing 

 them to settle spontaneously from pure saccharose solution of pH 

 6.0 the optimal point of agglutination was noted at the following 

 reactions (electrometric): pH 5.71, 5.79, 5.76 to 6.18, 5.38 to 5.80, 

 5.78, and 5.69 to 5.77. This shift toward a more acid zone runs 

 parallel with that observed in the precipitation of guinea pig globuUn 

 which has been washed as precipitate and redissolved by bringing to 

 pH 7.4 with NaOH. Precipitation then has its optimum between 

 pH 5.1 and 5.7." 



^ Guggenheimer, H., Z. Immunil'dtsjorsch. Orig., viii, 1910-11, 295. 

 * Coulter, C. B., /. Gen. Physiol., 1920-21, iii, 771, 



