Bob sighed. "The Mint men have been melting down a lot of silver, which was taken from a treasure-galleon on the Spanish Main. When it melts, certain fumes rise out of it—surely you know more on this than I—and the men who breathe in those vapors grow ill. There is only one remedy. Sir Isaac learnt of it from some German coiners he hired during the Great Recoinage. It is to drink milk from a human skull. Several of the Mint-men have lately gone down ill; so the call has been put out for skulls and milch-cows. What are you doing here, guv’nor?"