A tangle of protein (green) in this scanning electron micrograph of a brain cell of an Alzheimer's patient lies within the cytoplasm (blue) of the cell. The tangle consists of clumps of a toxic form of tau. Thomas J. Deerinck/Corbis hide caption

itoggle caption Thomas J. Deerinck/Corbis

A nurse adjusts the position of a patient's arm during dialysis treatment. The treatment requires trained staff that weren't readily available in the aftermath of Hurricane Sandy. Michael Donne/Science Source hide caption

itoggle caption Michael Donne/Science Source

This is a re-creation of a color plate from Interaction of Color, by Josef Albers. The two X's are are exactly the same — it's the different backgrounds that make them look like very different colors. Source: Josef Albers Interaction of Color hide caption

itoggle caption Source: Josef Albers Interaction of Color

Laundry detergent makers recently introduced miniature packets, but doctors across the country say children are confusing the tiny, brightly colored packets with candy and swallowing them. Pat Sullivan/Associated Press hide caption

itoggle caption Pat Sullivan/Associated Press

One of these penguins is not like the others — the chick in front is really a rover, designed by filmmakers and used by scientists to gather data. Huddle/John Downer Productions/BBC hide caption

itoggle caption Huddle/John Downer Productions/BBC

A python embryo turns its leg cells into a pair of penises. Researchers now believe that signals from the embryonic gut trigger the development of the penis in many different species. Patrick Tschopp/Harvard Medical School/Department of Genetics hide caption

itoggle caption Patrick Tschopp/Harvard Medical School/Department of Genetics