He conducted experimental studies on animal and human physiology particularly dealing with digestion, circulation, and the nervous system.

He was born at Shieldhall, Renfrewshire in Glasgow the son of Agnes Gillespie and her husband, Alexander Wilson.

Susannah had inherited wealth from her ancestor John Philip who had been governor of St Martin and laird of Almeriecloss, Angus.

He became a Fellow of the Royal Medical Society in 1791 and received his doctorate in 1792 with a thesis on an experimental esay on the process of digestion.

He conducted several experimented on himself, having orange juice and forcing himself to vomit it the next day to examine the state of digestion.

He moved to London after 1817 and lived in Cavendish Square from around 1824 and became more interested in diet and dyspepsia, possibly due to influential patients in the vicinity.