To see deeper than a millimeter inside a brain, scientists currently have to slice it into hundreds of thin sections and reconstruct the distorted neurons in 3-D on a computer. Dodt's solution is to first render the whole brain transparent by immersing it in an oily solution that prevents any light-scattering that might cloud the image. Then he slices with light instead of a knife, shining a laser on the tissue, which has been genetically engineered to fluoresce. Observed under a microscope, the result is a stunning 3-D view of neurons. "The technique could scale up considerably," says Dodt, who teaches full-time at the Vienna University of Technology. Next he'll try higher-resolution cameras, among other tweaks, to see all of the organs inside a mouse embryo.