Shot primarily in Hungary. The Arctic scenes were filmed in the Norwegian archipelago of Svalbard (Spitzbergen), just 500 miles south of the North Pole. This is the most northerly location that any TV series has ever shot.
Prologue: "The world is hell, and men are both the tormented souls and the devils within it." - Arthur Schopenhauer
Spirits of Squill could easily refer to a type of sea onion that has been in use medicinally since ancient Egyptian times. On board ship it could treat convulsions, asthma, or jaundice which is often a symptom of advanced scurvy. The doctor should know better than that.
Some of the medications listed by the surgeon were: boric acid, magnesium carbonate, ether, epsom salts, powdered rhubarb, calomel, and laudanum. Absinthe and blue vitriol were added at the apothecary.