Green’s Dictionary of Slang

used of one who is in good health, usu. in negative, e.g. Charles is not the plump currant.

c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Plump Current, I’m not plump Current, I am out of sorts.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Plump currant. I am not plump currant; I am out of sorts.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.