Heparin was discovered by Howell in 1916 and he showed that it increased the coagulation time of blood. No experimental work was done to prove whether it had any effect on thrombosis in blood-vessels. Thrombosis and obliteration of the lumen may result from injury of the intima of blood-vessels by various means, as Welch,2 Zurhelle,3 Schimmelbusch,4 and Zahn5 have shown. They have described the accumulation of platelets at the site of injury. Very soon leucocytes were added to the mass of platelets, and finally fibrin made its appearance, so that, ultimately, the ordinary blood-clotting processes were added to those of the earlier thrombus. As these changes have been fully described by these investigators, no attempt was made to repeat their work in our experiments.

As it was our object to study whether heparin would prevent these processes, different means of producing thrombi with moderate certainty were investigated. We found6 that superficial veins in the extremities of dogs may be moderately severely traumatized without producing thrombosis, but finally we developed a technique by which thrombosis could be produced in well over 80 per cent.