For most of history, the human heart has been regarded as a forbidden organ, too delicate to tamper with. In addition to medicine, I would include electricity. Electricity, like light, travels extremely fast at 300,000 kilometers per second. It flows easily through metal wires. In particular, copper and silver are very good conductors of electricity.
Electricity also generates heat as it flows through most objects.
It can be controlled and utilized easily using many different technologies. Electricity is very useful because it can be converted into many kinds of energy. Electricity can be converted in to light using light bulbs, and even heat by using heating coils. It can also be converted into motion or even stored chemical energy. Electricity also is used in commerce, agriculture, medicine, communications, entertainment, and a variety of other areas.