At the start of the 19th century, a ship sets sail from Bengal, India, carrying a most peculiar cargo... In this episode, we look at the development of the smallpox vaccine by an English country doctor, which rapidly eclipsed the earlier practice of inoculation. The cowpox vaccine represented an astonishing new development in public health, but also something of a logistical challenge - how to carry it long distances, across the sea? The answer would ignite a fierce culture war, and inextricably link the new technology to the age's great historical movements of power and empire.