James Johnson was an influential British writer on diseases of tropical climates in the first half of the nineteenth century. Born in Ireland, at the early age of 15 he became an apprentice to a surgeon-apothecary in Antrim for two years. After spending two further 2 years in Belfast, he moved to London for the surgeon's examination, which he passed in 1798. Immediately afterwards, he was appointed surgeons's mate on a naval vessel, on which he sailed to Newfoundland and Nova Scotia. In 1800 he took part in an expedition to Egypt and, in 1803, sailed for India. In 1814, Johnson attended the Duke of Clarence, and when Clarence became king was appointed as his physician extraordinary. He developed from that point careers as a physician and medical writer.