Throughout history, silver has been recognized as one of the most efficient germicides known. While an antibiotic can kill as many as a half-dozen different kinds of disease organisms, silver is known to kill some 650 species of bacteria or viruses simply by coming into contact with them. Particle size has been the only limiting factor to silver's effectiveness. Now through nano-technology, a rapidly growing science of producing and utilizing particles that measure in nanometers (1 billionth of a meter), silver can be used efficiently as an antimicrobial in medicines, filters, clothing and personal hygiene products.