Foci (singular focus) : Small groups of cells distinguishable, in appearance or histochemically, from the surrounding tissue: indicative of an early stage of a lesion that may lead to the formation of a neoplastic nodule
International Union of Pure and Applied Chemistry IUPAC, Glossary for Chemists of Terms Used in Toxicology, Prepared for publication by J.H. Duffus, NC., USA 1993. http://www.inchem.org/documents/harmproj/harmproj/ harmproj1.pdf & http://old.iupac.org/reports/1993/6509duffus/c.htm l, (IUPAC/ Tox - Amer) {107}