Augustus Pye was a trainee Healer at St Mungo's Hospital for Magical Maladies and Injuries in the Dai Llewellyn Ward. He was interested in Muggle healing techniques, and used stitches on Arthur Weasley when he was admitted to the hospital after he was attacked by Nagini. Presumably, Nagini's venom made Arthur's wounds impossible to heal in this manner, and caused the stitches to dissolve.