Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, 04 Nov. 2013. Web. 12 Nov. 2013. <http://www.cdc.gov/polio/>. "Google Images." Google Images. N.p., n.d. Web. 12 Nov. 2013. <http://www.google.com/imghp>. "Polio and Post-Polio Syndrome: MedlinePlus." U.S National Library of Medicine. U.S. National Library of Medicine, n.d. Web. 12 Nov. 2013. <http://www.nlm.nih.gov/medlineplus/polioandpostpoliosyndrome.html>. Staff, Mayo Clinic. "Definition." Mayo Clinic. Mayo Foundation for Medical Education and Research, 05 Mar. 2011. Web. 12 Nov. 2013. <http://www.mayoclinic.com/health/polio/DS00572>.