Once, in another age, the warriors who would become Plague Surgeons practised the healer's art in earnest, tending the wounds of their battle-brothers as sworn apothecaries of the Legion. That vocation has curdled utterly. A Plague Surgeon still carries the tools of medicine and still moves among his brothers in the heat of war, but what he practises now is closer to blasphemy than to healing.
His chief instrument is the Tainted Narthecium, a corroded gauntlet of blades, drills and injectors. With it he can knit a stricken Plague Marine back together and drive him onward, less mending the flesh than refusing to let it lie still, so that warriors fight on long after their bodies ought to have failed. Nurgle's gift of unnatural resilience flows through his ministrations, and the fallen are coaxed back to their feet to kill again.
Yet the Plague Surgeon's true fascination lies not in preservation but in disease. He regards each wounded foe and failing brother alike as a specimen, a vessel in which some novel contagion might be cultured and observed. Cold, curious and without mercy, he walks the battlefield harvesting samples and refining sicknesses, a physician who long ago traded the oath to do no harm for the promise of endless, fascinating rot.