FIBRINOGEN, fi'bri-n6-jen, a substance found in the plasma of the blood, and which brings about spontaneous coagulation of that fluid. It is also found in the lymph and in a number of other fluids of the body. Fibrinogen may be precipitated from the blood-plasma by the addition of magnesium sulphate or sodium chloride. It is soluble in dilute alkalis, and is precipitated from solutions in these weak alka lis by acetic acid. Fibrinogen is probably not a simple substance, but a mixture existing in loose combination of at least three substances. These as given by Schafer are fibrinogen proper, coagulating at 56° C., a globulin, de scribed by Hammarsten, and termed fibrino globulin, and a nucleoproteid. The relation ships of fibrinogen and fibrin and the blood ferment are expressed by Schifer as follows: That the coagulation of blood, that is, the transformation of fibrinogen into fibrin, re quires for its consummation the interaction of a nucleoproteid (prothrombin) and soluble lime salts, and the consequent production of a fer ment (thrombin) ; (2) that either nucleoproteid is not present appreciable amount in the plasma of circulating blood, or that the inter action in question is prevented from occurring within the blood vessels by some means at pres ent not understood; (3) that the nucleoproteid (prothrombin) appears, and the interaction oc curs, as soon as the blood is drawn and is al lowed to come into contact with a foreign sur face, the source of the nuceloproteid being in all probability mainly the leucocytes (and blood platelets?) ; (4) that, under certain circumstan ces and conditions, either the nucleoproteid does not appear in the plasma of drawn blood, or it appears, but the interaction between it and the lime salts is prevented or delayed; (5) that the nucleoproteid (prothrombin) appears in the plasma of circulating blood under certain con ditions, being in all probability shed from the red blood-corpuscles; and that when shed out under these conditions from the corpuscles, or when artificially injected into the vessels, it tends to interact with the lime-salts of the plasma and to form fibrin ferment (thrombin), intravascular coagulation being the result; (6) that, under other conditions, either the shed ding out of nucleoproteid from the corpuscles, or its interaction with the lime-salts of the plasma, may be altogether prevented and the blood rendered incoagulable, unless nucleopro teid be artificially added, or unless a modifica tion of the conditions is introduced which will permit of the interaction of the nucleoproteid with lime to form ferment; (7) that nucleo proteid (prothrombin) is incompetent, in the entire absence of lime-salts to promote the transformation of fibrinogen into fibrin; but, as a result of its interaction with lime-salts, it becomes transformed into a ferment (throm bin), which, under suitable conditions of tem perature and the like, produces fibrin; (8) that either the place of nucleoproteid in coagulation may be taken by certain albumoses, such as those found in snake-venom, and by certain artificial colloidal substances, such as those pre pared by Grimaux, or that such substances may act by setting free nucleoproteid from the leu cocytes and other elements in the blood or from the cells of the blood vessels, and thus indirectly promote coagulation.* See BLOOD; COAGULA
TION ; FIBBRIN ; GLOBULINS.