Experiments were carried out to determine whether or not sodium citrate in amounts ordinarily employed in clinical transfusions exerted a deleterious effect on the pneumococcidal properties of the blood. Observations were made first to test the action of citrate on the transfused blood. For this purpose sodium citrate in varying concentrations was added to rabbit serum-leucocyte mixtures seeded with pneumococci and containing specific immune serum. It was found that the presence of sodium citrate in concentrations of 0.5 per cent for the period of one hour had no depressant effect on the pneumococcidal action of the serum-leucocyte mixture. Higher concentrations up to 1 per cent produced only a very slight depression in activity. However, when allowed to remain in the serum-leucocyte mixtures for prolonged periods of time concentrations of sodium citrate above 0.1 per cent produced a definite diminution in their pneumococcidal activity. Tests made separately on the leucocytes and immune bodies in high dilution indicated that the serum or plasma protects them against injury by the citrate. The effect of sodium citrate in the circulation was next observed by testing the pneumococcidal promoting properties of the serum of rabbits before and after citrated blood transfusions. It was found that the injection of a quantity of citrate calculated to produce concentrations of as much as 0.3 per cent in the circulating blood, had no detectable harmful action on the pneumococcusdestroying properties of the rabbits blood. Larger quantities caused a marked injurious effect. As a further means of detecting any possible harmful action of sodium citrate on the anti-pneumococcus process of the body, a series of protective tests in mice were carried out using citrated immune whole blood or serum. It was found that 0.4 to 0.5 per cent citrate interfered in no way with their protective properties. The concentration of sodium citrate used in the above experiments which were found to be without detectable deleterious action on the pneumococcidal properties of the blood elements, are considerably less than those customarily employed in citrated blood transfusions.

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