The biggest hurdle to mass vaccination in the 19th century was keeping the virus alive out of the human body as the precious pus was being transported in sealed tubes to distant communities ravaging under smallpox. At a time when refrigeration, sterile containment, and asepsis were nonexistent, attempts were made to obtain the vaccine lymph dried onto silk threads or sealed between glass plates, but such methods proved unreliable on lengthy journeys and in warm climates. So when the need arose to vaccinate the remote Spanish colonies in America and Asia, Dr. Joseph Flores, the physician to King Charles IV of Spain, proposed an ingenious solution—carry the virus alive in human subjects.
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The corvette María Pita departs from the port of La Coruña in 1803. Engraving by Francisco Pérez.