He started with mouse embryos and graduated to goats, whose large mammary glands make better milk machines.

FORBES: Charlotte's Goat

Some had even transformed themselves into heart muscle, beating away in over half the mouse embryos treated.

ECONOMIST: Stem cells

Stem-cell research dates to 1981 and started out with mouse embryos, which researchers used to study the effects of individual genes and to try treating disease in mice.

FORBES: Magazine Article

But although he discovered the cells in mouse embryos, human embryos have them too, and that is leading to trouble as the desires of researchers butt up against the fears of ethicists.

ECONOMIST: The 2007 Nobel science prizes

Cells were taken from the tail of the mouse, then their genetic material extracted and used to create cloned embryos.

BBC: NEWS | Health | Mouse cloned to cure Parkinson's