"Functionally, however, the greatest difference between the two publications [Index Medicus and the Index-Catalogue] was that the Index-Catalogue was a government publication and Index Medicus was not. For its entire run, the Index-Catalogue was published by the Surgeon-General's Office of the US Army, while Index Medicus was privately published by a series of small publishers, who had difficulty making the work profitable. In this period (1879–1926), the Index-Catalogue had a secure source of funding, while Index Medicus was expected to be self-supporting. As Billings wrote in his introduction to the first volume of Index Medicus:

It has often been suggested that it is highly desirable that [the Index-Catalogue] should be supplemented by some current publication, which should show all recent works, together with articles in periodicals, arranged by subjects [emphasis in the original], but until quite lately no proper means have been available for such an undertaking. Now, however, Mr. F. Leypoldt, of New York City, proposes to undertake the publication of such a current medical bibliographical serial.

"The role of Leypoldt has been described in different ways, but it is undeniable that, between 1879 and 1926, Index Medicus had a number of publishers, including Leypoldt in New York, George Davis in Boston, and the Carnegie Foundation in Washington. There was even a period (1899–1902) when publication of Index Medicus ceased and was briefly replaced by a Paris publication called the Bibliographica Medica. There were also years, such as 1895–1899, when the title page mysteriously read only “Published by the Editors, New York and Boston.” Sometimes (as in 1879), publishers were listed for London, Paris, Leipzig, Amsterdam, and St. Petersburg, and would-be contributors were advised to submit their publications to these Europeans offices for inclusion in Index Medicus. A certain collection development objective is implied here: the introductory letter already cited made it clear that, after indexing, the publications would be added to the collections of the library" (S. J. Greenberg & P. E. Gallagher, "The great contribution: Index Medicus, Index-Catalogue, and IndexCat," J. Med. Libr. Assoc. 97(2009) 108–113).

A second series, edited by Fletcher and F. H. Garrison, vols. 1-6, 1921-27. In 1927 the Quarterly Cumulative Index to Current Medical Literature (12 vols., 1916-26) was amalgamated with the Index Medicus to form Quarterly Cumulative Index Medicus (1927-56) which, with No. 6777, was superseded in 1960 by a new monthly Index Medicus with an annual Cumulated Index Medicus. The gap 1900-02 was partly filled by Bibliographia Medica, 3 vols., Paris, 1900-1903, and by Index Medicus Novus, Vienna, Nos. 1-12, 1899; Nos. 1-3, 1900. The first three series of Index Medicus were reprinted New York, Johnson Reprint, 1967. Bibliographia Medica was reprinted New York, Johnson Reprint, 1972.

Fletcher, who was born in Bristol, England, assisted J.S. Billings in the creation of the Index-Catalogue (No. 6763).