'Unitary drives' revisited.
D000818:Animals; D001522:Behavior, Animal; D004032:Diet; D004326:Drinking; D004328:Drive; D004435:Eating; D004777:Environment; D005246:Feedback; D005247:Feeding Behavior; D006815:Hunger; D008954:Models, Biological; D012054:Reinforcement, Psychology; D013894:Thirst