Researchers have made a mouse see-through:

Disturbing - Scientists make a see-through mouse-dn25983-1_624-jpg

The reason?

They want to see inside with the greatest of ease!?

"Karl Deisseroth, at Stanford University, who developed the initial transparency technique is reportedly in the process of making a whole human brain transparent."

Gradinaru's group has also used the technique on human tissues. "We've cleared biopsies from skin cancer to identify what kind of cells are present," she says. The team were able to identify cancer cells and other tiny molecules present in the tissue at as well as current imaging techniques.

"Now we are working on mapping the nervous system," says Gradinaru. Working out exactly where nerves start and stop may help inform treatments that work by stimulating the nervous system, she says. "For example, there are instances where electrical stimulation is used to help treat Parkinson's, bladder control or pain and those electrical stimulators are applied to nerves throughout the body. Knowing exactly where those nerves run to and from, and their functions, would improve those treatments."

The method - (partially discussed)
[..] they pumped detergent around the entire mouse through its own circulatory systems.

By doing without the electric field, the team avoided tissue damage. The minimal swelling that occurred when the gel was absorbed was constrained by animal's bones and musculature.

Using this technique, Gradinaru's team was able to render peripheral organs transparent within two days and a whole mouse transparent within two weeks.

Acrylamide (the plastic used in soft contact lenses) is the magic ingredient pumped into the tissues.
Why a see-through mouse is a big deal for scientists - The Washington Post