ized terminology and alphanumeric designators for each chemical found in NLM's Medical Subject Headings (MeSH) and the MeSH tree structures.
Although there is subject and content overlap, each database serves a unique function, has a distinct subject emphasis, and indexes literature not available elsewhere. For example, the two prominent medical databases, NLM's Medline and Excerpta Medica's EMBASE, have only an approximate 36 percent content overlap. To serve the comprehensive goals of this study, it was decided to search all relevant databases in their entirety. A total of 46 online databases were searched, covering biomedical, toxicological, chemical, and regulatory information. As shown in Table 2-1, the majority of these databases were bibliographic, providing citations to scientific literature. Factual databases, Table 2-2, were also searched to provide toxicological and chemical information.
Online databases were developed in the mid-1960s, and few offer retrospective coverage. Identifying the literature published prior to this time required the use of a variety of sources. The volumes of Index Medicus covering the years 1917-1965 were an important bibliographic source. Reference lists of major review articles and books were also examined for relevant citations; several provided extensive reference lists (Goldman and Dacre, 1989; Gray, 1989; Papirmeister et al., 1991; Smith and Dunn, 1991; Somani and Babu, 1989). Document collection of published literature involved accessing the collections of the National Library of Medicine, the National Institutes of Health Library, the Himmelfarb Health Sciences Library of The George Washington University, and the National Research Council Library, as well as the use of interlibrary loans.
In conjunction with World War II (WWII) research on chemical warfare agents, scientists collected and reviewed the scientific literature and compiled bibliographies, which recorded the pre-WWII literature as well as ongoing military research. These include the bibliography for the Office of Scientific Research and Development, National Defense Research Committee's Summary Technical Report of Division 9: Chemical Warfare Agents and Related Chemical Problems; chapter reference lists in the three volumes of the National Research Council's Fasciculus on Chemical Warfare Medicine; and an unpublished bibliography compiled by the National Research Council's Committee on Treatment of Gas Casualties, entitled Bibliography of the Medical Aspects of Chemical Warfare: Published Literature.
Literature identification was an ongoing process throughout the study and, in addition to the above sources, input was received from