Definition: The primary lesion of syphilis, which begins at the site of cutaneous or mucosal infection after an interval of 10–30 days as a papule or area of infiltration, of dull red color, hard, and insensitive; the center usually becomes eroded or breaks down into an ulcer that heals slowly after 4–6 weeks. Finding Treponema pallidum on dark-field examination is diagnostic, except in oral ulcers, in which T. microdentium is normally present.
[Fr. indirectly from L. cancer]
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Examples: glitazone, GI cocktail, etc.