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When William was twenty-two, he graduated with the degrees of Doctor of Medicine and Master of Surgery. He had been the only student in McGill to take both his primary and degree examinations in the same year. He dreamed of working at the school one day.
In the meantime, he had to find a way to make a living. In 1872, William was appointed to work as a house doctor in Hamilton, Ontario, where he had first come across smallpox. McGill soon approached him with a job offer to become a lecturer of botany. Osler had politely refused since he knew little of the subject. Nearly one year later, they had re-approached him with the position of a medical lecturer at the school. He had then accepted. Osler had only been twenty-five, younger than many of his students earning him the nickname "Baby professor." After a mere one term, Osler had been promoted to the high status of Professor of the Institutes of Medicine. However, Osler had simultaneously acted as a private practitioner in Montreal and as a physician to the smallpox ward in Montreal General.
His very first original discovery had become an investigation into the deaths of several puppies at the Montreal Kennel Club in 1877. He had observed their living conditions and found a previously unknown parasite. The rare nematode had been named Oslerus osleri. This parasite causes verminous bronchitis in humans.
In September 1888, Osler officially accepted the job offer to teach from Johns Hopkins Medical University in Baltimore, Virginia. When the hospital opened on May 7, 1889, it was said to be the most anticipated hospital opening in American history. The founder, the late Johns Hopkins, had left a fund of an astounding three and a half million dollars to build the school. He is depicted in the Thomas Eakins painting; The Four Doctors alongside the three other doctors that helped shape the foundation of the school.
D. Appleton & Company, based in New York, had offered Osler a contract for publishing a book.