Which of the following substances, if introduced into the blood stream, would cause coagulation of blood at the site of its introduction?

Step-by-step solution

Thrombin acts as an enzyme and catalyses fibrinogen (a soluble plasma protein) into an insoluble fibre like polymer, fibrin. These fibres form a dense network upon the wound and trap blood corpuscles (WBCs, RBCs and platelets) and thus form a clot. Proteolytic cleavage of prothrombin generates thrombin, which converts fibrinogen into fibrin for clot formation. Fibrinogen is a protein produced by the liver which helps stop bleeding by helping blood clots to form. Heparin is used to prevent blood clots from forming.