Virology in order to immunize others. In 1717 Lady Mary Wortley Montagu observed the practice in Istanbul and attempted to popularize it in Britain, but encountered considerable resistance. In 1796 Edward Jenner developed a much safer method, using cowpox to successfully immunize a young boy against smallpox, and this practice was widely adopted. Vaccinations against other viral diseases followed, including the successful rabies vaccination by Louis Pasteur in 1886. The nature of viruses however was not clear to these researchers. In 1892, the Russian biologist Dmitry Ivanovsky used a Chamberland filter to try to isolate the bacteria that caused tobacco mosaic
Mozart and smallpox both children's illness to contend with, the Mozarts spent a total of four months away from Vienna. They eventually returned there and were received in the Imperial court on 19 January, 1768. The Empress, who had by now lost three children to smallpox, conversed with Frau Mozart about the disease. The remainder of the trip was not especially successful. Leopold apparently misinterpreted a chance remark of the Emperor as a firm invitation for Wolfgang to compose an opera; this resulted in Wolfgang writing "La finta semplice". However, the opera went unperformed in Vienna; the singers and musicians did not like