The articles below are available on the Internet.
Birch, Hayley, Colin Stuart, and Mun Keat Looi. 2013. The 20 Big Questions in Science. The Guardian (August 31, 2013). http://www.theguardian.com/science/2013/sep/01/20-big-questions-in-science (accessed February 17, 2014).
Murphy, Dominic. 2009. Concepts of Disease and Health. The Stanford Encyclopedia of Philosophy (Summer 2009). http://plato.stanford.edu/archives/sum2009/entries/health-disease (accessed February 17, 2014).