Viruses
Viruses are tiny, tiny organisms…smaller than bacteria and smaller than many cells in your body. But they can cause you to get sick…and viruses can be hard to fight off! So, what are viruses? How does your body deal with them? Why do they make you sick? Learn more…
http://www.ucmp.berkeley.edu/alllife/virus.html
http://www.collegian.psu.edu/archive/2001/10/10-30-01tdc/10-30-01dscihealth-column-2.aspÂ