potential reactors to avoid the issue. The results of toxoid use in Hamilton, Ontario were particularly significant and widely recognized. In 1922, there were 747 cases and 32 deaths due to diphtheria in Hamilton. By 1927, the numbers had fallen to 11 cases and 1 death. In 1931, there were only 5 cases and no deaths. A year later, there was a single case and no deaths. Development of heparin: 1928-1930s Heparin is a blood thinner (anticoagulant), originally discovered in 1916 by Jay McLean and William Henry Howell at Johns Hopkins University. However, the crude substance was toxic and could only be extracted in small quantities. As co-discoverer of insulin Charles Best returned from his postgraduate studies in Europe to continue as Connaught's Assistant Director, he began a program in 1928 to purify heparin for clinical use. This direction of development benefitted from Connaught's experience with insulin production and ongoing arrangements with Canadian meat processors to obtain research material. In 1933, Arthur Charles and David Scott published the first papers on increasing the yield of heparin by rotting source tissues. By 1936, Charles and Scott managed to crystallise the heparin extract into a dry form that could be administered in a salt solution. This became Connaught' second product, after insulin, to be recognised as an international standard. Gordon Murray, a prominent surgeon based at Toronto General Hospital, demonstrated that heparin effectively cleared up internal blood clots and that it showed promise in dangerous operations in which blood would otherwise thicken too quickly. Initial clinical trials, begun in April 1937 or slightly earlier with cruder forms, involved hundreds of complex surgical cases "in which heparin played an essential and often dramatic life-saving role". The advances that made heparin a safe, easily available and effective anticoagulant were welcomed internationally, and lay the foundation for vascular surgery, organ transplants, and open-heart surgery. The developments also allowed Gordon Murray to pioneer the artificial kidney in North America. World War II: 1939-1945 Canada entered World War II on September 10, 1939. In 1940, Connaught lost its founder and director Dr. John G. FitzGerald to mental health struggles. Robert Defries, who had already been leading much of the Labs' efforts through the 1930s, stepped in to fill the role as director of Connaught Laboratories and of the School of Hygiene. This period saw the rapid expansion of Connaught's research capacities to accommodate the military demands of