the first doctor to do so. In 1907 Hirschfelder and A. G. Gibson independently discovered what is now called the "third heart sound". During the spring of 1913, after Hirschfelder wrote a paper on "Diuretics in Cardiovascular Disease" and presented it at the American Medical Association meeting, Charles Lyman Green, a professor of pharmacology at the University of Minnesota College of Medical Sciences, offered Hirschfelder a professorship position in pharmacology at Minnesota. Hirschfelder accepted the position and moved to Minneapolis, Minnesota where he pursued research on local anesthesia. He remained as the first director of the Department of Pharmacology until 1942. During World War I, Hirschfelder organized and taught school for navy pharmacists mates at the University of Minnesota. He also developed an improve a cloth designed to kill lice with brominated and chlorinated cresol compounds that would last for thirteen days, an improvement from the ordinary cresol and naphthol treatment, which only lasted for one day. Furthering his war effort, Hirschfelder worked as a pharmacologist in the Chemical Warfare Service research unit at Johns Hopkins in 1918 and after the war served as a board member of the Board of Consultants of the Chemical Warfare Service at Edgewood Arsenal from 1922 to 1925. Medicine Research Johns Hopkins University Hirschfelder dug into the cardiac world upon returning to Johns Hopkins by studying how cardiac nerves behaved during a third-degree atrioventricular block (AV block- also known as a complete heart block). In this condition, the ability of the heart to relay electrical signals from the atria to the ventricles is compromised. Hirschfelder and one of Johns Hopkins's physiologists, Joseph Erlanger, worked together to develop important methods in cardiovascular medicine and became the first doctor in the United States to use an EKG in human studies. Hirschfelder was able to prove, through an experiment on dogs, that the dyspnea that arises due to heart failure occurs when the pulmonary capillaries and veins become inactive. When this occurs, the flexibility of the lungs is inhibited causing the volume of the lungs to increase and therefore diminish flow of air through the lungs. In a separate experiment to find factors that affected a complete stop of the ventricles, Hirschfelder and Erlanger discovered that when a clamp was tightened over the auriculoventricular (atrialventricular) bundle suddenly a complete stoppage of the ventricles occurred. On the other hand, when the clamps were tightened gradually, the heart passed