The action of thrombin on fibrinogen.

THE solutions of fibrinogen, thrombin and sodium chloride employed in these experiments contained about 0 5 % of tri-sodium citrate. As source of fibrinogen human plasma was ordinarily used, being prepared by mixing 12 cc. of blood, immediately after withdrawal from a vein of the forearm, with 1 cc. of 0-85 % sodium chloride solution to which 013 g. sodium citrate had been added. After centrifugalisation the plasma was pipetted off and stored at 0°. In a few experiments fibrinogen was precipitated by pouring human plasma into twenty volumes of distilled water through which a stream of carbon dioxide had been passed, the precipitate being separated by centrifugalisation and then redissolved in citrated 0'85 %, sodium chloride solution. As source of thrombin freshly prepared whipped blood, to which 1 % of sodium citrate had been added as soon as separation of fibrin was completed, was used in a few experiments. As, however, the range of concentration of thrombin obtainable in this wav was small, in most experiments the thrombin employed consisted of the venom of Echis carinatus1 dissolved in 0-85 % sodium chloride solution, to which 0 5 % of sodium citrate had been added [Barratt, 1915]; the limit of utility of this form of thrombin was about 1 in 30,000,000 and the highest concentration used rarely exceeded 1 in 3000; it was completely destroyed by heating to 750 for ten minutes. Dark background illumination was obtained by means of a paraboloid condenser with central stop, an arc lamp being used as source of light. Coagulation was usually studied at room temperature, the mixture of fibrinogen and thrombin, which formed the subject of observation, being placed upon a glass slide, within an area ringed with vaseline, and closed bv a coverslip: the thickness of the layer of fluid examined was usually about 50,u. Occasionally coagulation was carried out in small glass tubes.