in 1765 he received his md and established a medical practice in birmingham, and shared a house with the physician john ash who was the chief campaigner for the birmingham infirmary. small was boulton's physician and became a close friend of erasmus darwin, thomas day, james keir, james watt, anna seward and others connected with the lunar society. he was one of the best-liked members of the society and an active contributor to their debates.