The leading cause of death for soldiers on all sides of the War of 1898 was not combat but diseases such as typhoid and yellow fever. As a result, the United States Army formed research organizations, such as the Yellow Fever Commission, to study infectious diseases. Physician and commission member Jesse W. Lazear deliberately contracted yellow fever to test Carlos Finlay’s theory that the disease was spread by mosquitos. The chart tracks Lazear’s temperatures from September 19 until his death on September 25, 1900.