A microscopy image of a rat pancreas shows the insulin-making cells in green. Masur/Wikimedia.org hide caption

itoggle caption Masur/Wikimedia.org

SWAT team members stand guard on the campus of Massachusetts General Hospital following the explosions at the finish line of the Boston Marathon. Michael Dwyer/AP hide caption

itoggle caption Michael Dwyer/AP

In this Jan. 18 photo provided by the NYU Langone Medical Center, a technician examines mice to determine their health at the hospital's complex in New York. New York University/AP hide caption

itoggle caption New York University/AP

Layton, Utah police department employees Holly Plotnick and Shanae Perez pack discarded medications from a collection bin in the lobby in January 2010. Mike Stark/AP hide caption

itoggle caption Mike Stark/AP

The bean of the castor-oil plant, Ricinus communis, is used in the production of castor vegetable oil and ricin, a poison. Sasha Vasko/via Flickr hide caption

itoggle caption Sasha Vasko/via Flickr