Clara Maass (1876-1901) was a contract nurse with the U.S. Army in Florida, Georgia and Cuba during the Spanish American War. She saw how many deaths occurred not because of combat, but from yellow fever. The cause of the disease was unknown and Clara volunteered for a medical experiment to help determine how it was spread. She allowed herself to be bitten by mosquitoes, which were suspected to transmit the disease. She recovered the first time she contracted the disease, but after volunteering a second time she succumbed to the illness. Her sacrifice helped determine how yellow fever was spread. In 1976, the centennial of her birth, Clara was inducted into the American Nurses Association Hall of Fame and honored on a stamp by the Postal Service.