JOHN, M.D. (1709-1779).-Poet, _s._ of the minister of Castleton, Roxburghshire, studied medicine, which he practised in London. He is remembered as the friend of Thomson, Mallet, and other literary celebrities of the time, and as the author of a poem on _The Art of Preserving Health_, which appeared in 1744, and in which a somewhat unpromising