Green’s Dictionary of Slang

jack (in the box) n.

also the jack
[rhy. sl. = pox n.1 (3)]

venereal disease.

Horn Book 43: [He] says: ‘You know I’ve got the “Horse and Trap”.’ ‘Have you?’ says the other, ‘well, I’ve got the “Jack”’.
Partridge DSUE: .
S.J. Baker Papers Mitchell Lib. MS 165 Box 2 Bundle iv File 8 jack—syphilis.
[Aus]T.A.G. Hungerford Sowers of Wind 3: Penicillin’ll take care of that. They reckon they just pump you full of it, and bingo! No more jack!
[UK]J. Franklyn Dict. of Rhy. Sl.
Hogbottel & Ffuckes Snatches & Lays 75: He’s waiting to give her a belt up the back, But without a french letter he might get the jack.
[Aus]Adamson & Hanford Zimmer’s Essay 56: No worries about jack in this one. A virgin, no worries.
D.R. Stuart Crank back on Roller 199: Ah, the poor bastard got a jack in Tassie before we’d been in camp a month . . . Fuck a dog on a chain, the bloody fool [AND].
[UK]Partridge DSUE (8th edn) 607: since ca. 1870.
[Aus]B. Ellem Doing Time 191: jack: [...] ‘the jack’ refers to a venereal disease.
N. Medcalf Rifleman 73: Got malaria, beri-beri, malnutrition and probably a dose of jack [AND].
[Aus]R.G. Barratt ‘Who’s Jack of Robbo?’ in What Do You Reckon (1997) [ebook] I got the jack years ago and had to go to the VD clinic.
[UK]R. Puxley Cockney Rabbit.
[UK]B. Dark Dirty Cockney Rhy. Sl.