It has been stated above that sodium citrate introduced into the circulation in small quantities, such as are sufficient for anticoagulant purposes, is non-toxic to man. In the light, however, of the extended experience of the last four years, it is seen to be possible that this statement may not be quite literally true. Probably there is an individual variation in the tolerance of different people to sodium citrate. Certainly in some cases a reaction follows the injection of citrated blood. The symptoms of this reaction are a slight headache, a rise in temperature to two or three degrees above normal, sometimes accompanied by a rigor or a sensation of chill, and an increase in the pulse rate. The effect is, however, always very transitory, lasting only two or three hours, and is never, in my own experience, attended by any symptoms which need give rise to anxiety for the patient’s welfare; nor does it in any way prejudice the therapeutic results of the transfusion. That the reaction is caused by the citrate and not by another constituent of the transfused blood has been believed by several observers. In a case seen by the writer a slight citrate reaction occurred in a youth who acted as blood donor. The transfusion was carried out by a modification of the syringe method, which involved the injection at intervals of a syringeful of citrate solution into the donor’s circulation. The possibility that the reaction was produced by another factor was therefore not present in this instance.