care of her at home while she suffered from Alzheimer's disease. After the United States declared war on Germany in April 1917, Heidelberger was commissioned in the Sanitary Corps and assigned to the Rockefeller Institute. He continued to work with Jacobs, a collaboration that lasted more than nine years and produced 44 papers. They synthesized many chemotherapeutical drugs, namely aromatic arsenicals, for the treatment for infectious diseases, in particular syphilis and African sleeping sickness. In 1919 they developed a variant of Paul Ehrlich's "magic bullet" for syphilis, Salvarsan, which proved effective against trypanosomes, the parasites that cause African sleeping sickness. Variants of tryparsamide, as Flexner named it, continue to be administered today. In 1953 the king of Belgium, colonial ruler of parts of Africa in which African sleeping sickness had been endemic, honored Heidelberger and Jacobs for their discovery. In 1921 Heidelberger transferred to the laboratory of Donald D. Van Slyke at the Rockefeller hospital, where he spent the next two years developing a method for preparing large quantities of purified oxyhemoglobin, with its oxygen-carrying capacity intact, for Van Slyke's studies of the uptake and release of oxygen in the blood. When Karl Landsteiner, the famous Austrian immunologist and discoverer of human blood groups, arrived at the institute in 1922, Heidelberger embarked with him on studies of the antigenic properties of different types of hemoglobin. Throughout his life Heidelberger was proud to state that he first learned immunology from Landsteiner. During this time Heidelberger was approached by the bacteriologist Oswald Avery to help him elucidate the chemistry of the "specific soluble substance" Avery and Alphonse R. Dochez had found in the spherical capsule that envelops pneumococcus and many other species of bacteria. In 1923, Heidelberger and Avery reported that this capsular substance, which determined the specific type of pneumococcus and, with it, its virulence, consisted of polysaccharides, carbohydrate molecules made up of more than three monosaccharide units. Their discovery for the first time established a relationship between chemical constitution and immunological specificity of antigens, thereby putting the field of immunology on a firm biochemical footing. It also disproved prevailing assumptions among scientists that only proteins could act as antigens. Heidelberger devoted the rest of his career largely to pursuing the consequences of his and Avery's seminal discovery. He identified and analyzed the structure of different pneumococcal polysaccharides—over one hundred have since been found—as well as of other microorganisms, and studied