cullen was a beloved teacher, and many of his students became influential figures in their own right. his best-known students—many of whom continued to correspond with him during his long life—included (in addition to joseph black, who became his colleague) benjamin rush, a central figure in the founding of the united states of america; john morgan, who founded the first medical school in the american colonies (the medical school at the college of philadelphia); william withering, the discoverer of digitalis; sir gilbert blane, medical reformer of the royal navy; and john coakley lettsom, the philanthropist and founder of the medical society of london.