The Hirsh Library uses the National Library of Medicine Classification for its call numbers in clinical sciences, dentistry and medicine. The NLM Classification is a system of mixed notation, where letters denote disciplines, specialties, systems, or other broad subjects, and numbers specify more particular subjects or types of works. For instance, anatomical atlases would be shelved at QS 17, while general psychiatric textbooks would be shelved at WM 100. An interactive index of the complete system is available at NLM: Outline of the NLM Classification.