Horse serum, kept for 2 hours at 38°C. in the presence of one-fifth its volume of a suspension of 0.5 per cent of pararabin inphysiological salt solution and then freed by means of centrifugalization and filtration from the pararabin produced when injected in appropriate doses into a normal rabbit, a considerable and prolonged fall of the blood pressure, a distinct retardation in the coagulation of the carotid blood, and sometimes, in addition, acceleration of the respiratory rate and the expulsion of numerous scybala; that is, the various symptoms observed to occur after the intravenous injection of horse serum in sero-anaphylactized rabbits.

If the horse serum is first heated for 30 minutes to 56°C. and then treated with pararabin in the manner described above, the intravenous injection of this serum into a normal rabbit exerts no more action on the arterial pressure, the coagulability of the arterial blood, the respiratory rate, and the intestinal activity, than does normal horse serum when introduced into the vein of a normal rabbit.

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