by Bingley
The Dryden translation of paragraph 6 of Plutarch's Life of Marius reads:
Marius is praised for both temperance and endurance, of which latter he gave a decided instance in an operation of surgery. For having, as it seems, both his legs full of great tumors, and disliking the deformity, he determined to put himself into the hands of an operator; when, without being tied, he stretched out one of his legs, and silently, without changing countenance, endured most excessive torments in the cutting, never either flinching or complaining; but when the surgeon went to the other, he declined to have it done, saying, "I see the cure is not worth the pain."
According to the Perrin translation on LacusCurtius and Robin Waterfield's
translation in Roman Lives: A Selection of Eight Lives (Oxford World's Classics) (page 127), however, what Marius was
actually suffering from were varicose veins.
LacusCurtius refers us to a description of the operation by Celsus, an encyclopedic writer from the first century AD, of whom we do not know much. His only surviving work is De Medicina. More on Aulus (Aurelius?) Cornelius Celsus at LacusCurtius, and a wiki stub.
Pictures of surgical instruments can be seen here (scroll down to "Tile Cautery").
Postscript from Irene: Here is another source and related image of a ferrum candens.
The above mentioned volume on Plutarch contains the biographies of Cato the Elder, Aemilius Paullus, Tiberius and Gaius Gracchus, Marius, Sulla, Pompey, Caesar, and Antony.