In 1836 Surgeon General Joseph Lovell established a small collection of medical books for the use of his staff. This was the origin of the “Surgeon General’s Library.” John Shaw Billings did much to develop the library; he planned and started the Index Catalogue, the first large-scale subject index of any library, and the first truly comprehensive subject index of the published literature any science. Four years prior to the beginning of publication of the Index Catalogue Billings issued a Specimen Fasciculus of a Catalogue of the National Medical Library Under the Direction of the Surgeon-General, United States Army (Washington, 1876). In addition to showing the ambitious nature of his cataloguing plans, the fasciculus shows that Billings viewed the Library of the Surgeon General's Office as a national medical library. Series 1-4 indexes about 3,000,000 books, journal articles, and pamphlets. In the 5th series only monographs and theses are included. For continuation see Nos. 6784, 6786.9. In 1952 the name of the library was changed to Armed Forces Medical Library; it became the National Library of Medicine in 1956. See S. J. Greenberg & P. E. Gallagher, "The great contribution: Index Medicus, Index-Catalogue, and IndexCat," J. Med. Libr. Assoc. 97 (2009) 108–113.
The Index-catalogue is available online from the National Library of Medicine at this link.