THE AGGLUTINATION OF RED BLOOD CELLS IN THE 

 PRESENCE OF BLOOD SERA. 



By CALVIN B. COULTER * 

 (From the Hoagland Laboratory, Brooklyn) 



(Received for publication, January 6, 1922.) 



The optimum for the agglutination of normal sheep cells in iso- 

 tonic saccharose solution has been given as pH 4.75.^ To correct 

 a possible error in the colorimetric measurements originally employed 

 electrometric determinations have been made in a similar series of 

 experiments in which graduated amounts of n/10 to n/40 HCl have 

 been added to suspensions of red blood cells in saccharose solution 

 and measurements made of the reaction of the supernatant fluid 

 from which the cells have been removed 15 to 30 minutes after the 

 addition of acid. The average pH 4.76 of the following values thus 

 found corresponds closely with the result of the colorimetric method : 

 pH 4.55, 4.57, 4.79, 4.90, and 5.03. 



Cells sensitized with approximately 10 units of immune rabbit 

 serum at pH 5.3, the optimum for combination of the cells with the 

 immune sensitizer- and washed with pure saccharose solution at the 

 same reaction agglutinate most promptly at the following reactions 

 in a series of experiments: pH 5.22 to 5.45, 5.26, and 5.06 to 5.30. 

 The average is pH 5.26. The colorimetric method had given from a 

 larger series the value pH 5.3. If the cells be not washed after the 

 addition of immune serum which was present in a concentration of 

 0.5 per cent by volume, the optimum occurs at a slightly higher figure, 

 pLI 5.5 approximately. 



If a similar small volume of active normal rabbit serum be added 

 to the cells in place of the immune serum, the optimum for agglutina- 

 tion occurs at the same point, pH 5.5. 



* Van Cott Fellow in Pathology. 

 1 Coulter, C. B., J. Gen. Physiol, 1920-21, iii, 309. 

 'Coulter, C. B., J. Gen. Physiol, 1920-21, iii, 513. 



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