Modifications have been introduced, such as that of Vincent, who uses an attachment with a needle instead of the glass cannula point. This obviates some of the objections, but introduces other difficulties, such as the necessity for coating the inside of the needle with paraffin wax. The technique can certainly be acquired, and the method has rendered excellent service in the past, but it has no obvious advantages except the uncertain one of avoiding chemical treatment of the blood. =Transfusion with Anticoagulants.=--It will have become evident from the descriptions of the transfusion of whole blood already given, how great a difficulty is introduced into the technique of these methods by the physiological process of clotting in blood outside the body. It is clear how much the process of transfusion would be simplified if the clotting were to be prevented. Something has already been said in the historical sketch of the various means by which this problem was attacked, and it need only be stated here that the most suitable substance for this purpose has been found to be sodium citrate. This method was introduced by Lewisohn as recently as 1915, and it soon became the method of choice among most of those who tried it. The process of the formation of a blood clot has always been one of the great problems of physiology, and numerous theories have been propounded to explain it. The theory accepted at the present time regards the process as a complicated one depending on the presence in the blood of a number of different factors. This theoretical explanation may be represented diagrammatically as follows: [Illustration: Plasma Tissues and Platelets | \ \_______________ \ / | \ \ \ / | \ \ \ / | Prothrombin Ca Salts Thrombokinase | \_________ \ / | \ \ / | \ \ / Fibrinogen Thrombin \ / \ ___________/ \ / Fibrin ]