Green’s Dictionary of Slang

white nurse n.

(drugs) any form of powdered white drugs.

1936		D. Maurer ‘Argot of the Und. Narcotic Addict’ Pt 1 in AS XI:2 127/2: White nurse. A term loosely used, like several others, to mean cocaine, heroin, or more frequently, morphine.
1959		J.E. Schmidt Narcotics Lingo and Lore 191: White nurse – Morphine.
1989		J. Morton Lowspeak 149: White nurse – morphine.
2001		ONDCP Street Terms 22: White nurse — Heroin.

In phrases

chase the (white) nurse (v.)

to be addicted to morphine.

1959

J.E. Schmidt Narcotics Lingo and Lore.