Special Update: More Sources Of Adam
While extracting Adam from Little Sisters is still an option in BioShock 2, there are now more ways to collect the precious material. Look carefully and you'll find Adam slugs stuck to various surfaces of the ocean floor. Simply pick them up for a small dose. Another small hit of Adam can be extracted from Big Sisters (yes, there is more than one!). After clearing all Little Sisters from a level, a Big Sister arrives as the last line of defense for Rapture's Adam supply. Once a Big Sister is defeated, you can loot the twiggy, mechanical corpse for the slug. Every bit counts.

Bioshock 2 Walkthrough