Through an examination of the life and remarkable achievements of Sir William Brooke O'Shaughnessy, this book reveals a great deal about both medical and scientific innovation in the nineteenth century. It traces O'Shaughnessy's career. At the age of twenty-three in 1831 he identified the physiological cause of death from cholera and recommended intravenous saline as the cure in the face of the contemporary medical belief in bloodletting. In 1833 as an Assistant Surgeon of the East India Company, and later as Professor of Chemistry in the new Calcutta Medical School, he saw the possibilities of native plants and studied several. These included cannabis, about which he published a detailed analysis which led to the introduction of cannabis as a pharmaceutical product in the West, a use which continued until the mid-twentieth century. Later he pioneered telegraphy, first with an experimental line in Calcutta and then, as superintendent of Indian Telegraphs, he supervised the successful construction of several thousand miles of telegraph across India, thereby enabling closer control of India by the colonial power. Throughout, besides giving details of O'Shaughnessy's personal life, the book sets his work and achievements in their wider context.