These databases are the main ones you'll need to research medicine and medical history. Mouse over the little circle icon next to the link to get a description of each database and what it contains. Note that they're not in order of relevance: for any medical topic, always start with PubMed. For any history topic, go to Historical Abstracts.
Here, again, mouse over the circle icon next to the links to see descriptions of the databases and what they contain.