He is laid up in Job’s dock; i.e. in a salivation. The apartments for the foul or venereal patients in St. Bartholomew’s hospital, are called Job’s ward.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Job’s Comforter * JobationNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes