The Agglutination of R E D Blood Cells in the Presence of Blood Sera. by Calvin B. Coulter*

The optimum for the agglutination of normal sheep cells in isotonic saccharose solution has been given as pH 4.75.1 To correct a possible error in the colorlmetric measurements originally employed electrometric determinations have been made in a similar series of experiments in which graduated amounts of rr/10 to N/40 HC1 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, 5.25, and 5.06 to 5.30. The average is pH 5.25. 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, pH 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 agglutination occurs at the same point, pH 5.5.