he expansion of the MeSH tree structure from nine to eleven levels has allowed for a long-awaited revision concerning the heading ANIMALS, the check tag ANIMAL, and related headings. NLM^® is highlighting this change in a separate article, because the revision will result in a vast improvement in the representation of knowldege in the tree structures. However, its impact on searching PubMed^® is actually small. Here is a summary of the changes for 2004:

1. The old descriptor ANIMALS will be changed to ANIMAL POPULATION GROUPS. It will retain all indented terms.
2. The check tag ANIMAL will be changed to a new descriptor ANIMALS. It will function as both a descriptor and a check tag and will be treed at B1. The singular word Animal will map to this new plural heading.
3. The old descriptors B1 INVERTEBRATES and B2 VERTEBRATES will be treed under ANIMALS.
4. The old B5 ALGAE AND FUNGI will be split into two descriptors. ALGAE will become B2 and FUNGI will remain at B5.

[Table corrected November 21, 2003.]

Below are the revised descriptors with scope notes and cross references:

Animals
Unicellular or multicellular, heterotrophic organisms that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain Eukarya.

[Note: As "Animal" will be retained as an Entry Term (cross reference) for "Animals" (see X Animal above), PubMed searches for Animal or Animal [MH] will map to the new term, "Animals."]

Animal Population Groups
Animals grouped according to ecological, morphological or genetic populations.

PubMed users who have stored Cubby searches containing the 2003 descriptor ANIMALS or check tag ANIMAL are advised to make the appropriate changes in November 2003, to prepare for the 2004 vocabulary.

Helpful hints for PubMed searchers:

1. Searches for the old plural heading ANIMALS will need to be adjusted to use the new heading ANIMAL POPULATION GROUPS. This heading is used infrequently in MEDLINE because it is a general term (occurs fewer than 2,000 times). Indexers would use its more specific indented terms such as ANIMALS, DOMESTIC; ANIMALS, NEWBORN; and ANIMALS, POISONOUS. The explosion of ANIMALS [mh] in 2003 retrieves over 585,000 hits.
2. Searches for the old singular heading ANIMAL probably do not need to be adjusted. The singular form of the word will map to the preferred plural form of the word. This concept continues to represent the "check tag use" for labeling clinical and experimental studies on animals and occurs frequently in MEDLINE (about 3.4 million times).
   
   Note: Some headings indented under the new Animal Population Groups heading (which itself is indented under Animals for 2004) are not always coordinated with the check tag Animals, e.g., Chimera; Organisms, Genetically Modified. Such headings may describe either animals or plants, for instance. Be advised that using the new Animals heading in 2004 will retrieve some extra citations that are not indexed to Animals because of the automatic explosion of the tree; the same result has been true in the past because the Automatic Term Mapping for Animal has included both Animal and Animals, two different MeSH headings up until 2004 MeSH.
3. The Limit in PubMed will remain the same with the choices in the singular form, i.e., Human or Animal. The plural HUMANS will be an entry term for HUMAN, as well. Whether a searcher chooses from the Limit box or types the singular or plural forms of either of these concepts directly in the query box, PubMed will retrieve the same MeSH Heading hits.
4. ANIMALS will continue to retrieve all MEDLINE citations previously indexed to and retrieved by ANIMAL back through 1966.

Savage A. 2004 MeSH Changes to the Category B Organisms Tree and the Check Tag Animal. NLM Tech Bull. 2003 Sep-Oct;(334):e5.