Corrected entry: The Doctor cures The Flesh by disinfecting them with a cocktail of the various cures created by the Cat Nuns. However, surely these cures would have no effect on The Flesh, as they were being used to test those very things? The diseases that The Flesh had would be the ones the nuns were yet to find the cure for, so even if the cocktail did remove some of the diseases it couldn't remove all of them.
Movie Nut
7th Jun 2017
Correction: The Flesh would respond to certain cures, depending on the particular infection. The Nuns were testing in very small, controlled batches. However, the strength of the cures in combination would have a positive effect.
Movie Nut