Complex sentence: Defoe notes that when a regular treatment regimen was found, (a serrated knife that could more neatly lance abscesses invented by a butcher), and more remained ill instead of dying, there were more ill than ever there were before the epidemic began.
Split into simpler sentences: Defoe notes that when a regular treatment regimen was found, (a serrated knife that could more neatly lance abscesses was invented by a butcher), more remained ill instead of dying. There were then more ill than ever there were before the epidemic began.