One of the most interesting and challenging developments in the field of the biologic sciences in recent years has been the recognition, isolation and, finally, synthesis of the substance causing hemorrhagic sweet clover disease in cattle, the dicoumarin 3,3′-methylene-bis-(4-hydroxycoumarin). We must give full credit for this contribution to two keen students of veterinary medicine, Schofield1and Roderick,2and to an outstanding agricultural chemist, Karl Paul Link. Schofield in Canada and Roderick at the North Dakota Agricultural Experimental Station studied and quite accurately analyzed the factors responsible for this phenomenon in cattle and rabbits. They pointed out that, whereas normal sweet clover silage produced no damage, spoiled sweet clover resulted in hemorrhagic tendencies and often in death. In 1934 Prof. Karl Paul Link and his associates at the Wisconsin Agricultural Experimental station of the University of Wisconsin undertook thetask of identifying the hemorrhagic factor in spoiled sweet clover.