Midi-chlorian/Legends

Midichlorians were microscopic life forms that existed inside the cells of all living things. While they were not the Force itself, they formed a link to it, acting as a sort of sensory organ through which it could be perceived. Midi-chlorians enabled the perception of the Force just as having eyes allowed people to see light or having ears allowed them to interpret vibrations as sound. If an individual had enough midi-chlorians in their body they could use them to communicate with the Force. In essence, midi-chlorians were the connection between a being’s mind and the Force, enabling certain sentients to intentionally manipulate it, or allow themselves to be manipulated by it.

A high midi-chlorian count was usually an indication of Force-sensitivity, meaning that the creature had the potential to become a Jedi. The Jedi Order was always on the lookout for Force-sensitives, who would be brought to the Jedi Temple and inducted into the ways of the Force. To further this goal, the Jedi learned how to quiet their minds and focus, so they would be able to sense the midi-chlorians that lay inside of other creatures. Once a being was suspected of having a high midi-chlorian count, a simple blood test could be administered to determine a definite amount.

During the reign of the Galactic Empire, midi-chlorian tests were performed to root out Force-sensitives and Jedi in hiding. Such individuals were rarely heard from again. In response, an underground trade of drugs and blood treatments sprang up that could supposedly fool a test or lower one's count; however, they were largely ineffective.

Midi-chlorian research
The Rakata were thought to have experimented with medically transferring midi-chlorians into other beings in an attempt to transfer Force-sensitivity. They supplanted the genes responsible for midi-chlorians from Force-sensitives into their own genetic code to try and help their race 'remember' forgotten Force abilities. It is not known whether these experiments had any success, as the Rakata believed it would still take many generations for the experiment to be complete.

Millennia later, scientists had been known to increase the midi-chlorian count of normal individuals on Vjun by artificial means. However, this led to many extremely Force-sensitive people who did not know how to control their power, and in turn, many of these Force-enhanced beings went insane. The Malreaux family was an example: Whirry Malreaux was a housewife who read the future in broken things and went insane after the death of her father. However, her son Whie Malreaux was taken away by the Jedi to begin Jedi training, and was spared from losing his mind. Whie also had premonitions and dreams of the future, similar to those of his mother and Anakin Skywalker.

When Supreme Chancellor Palpatine told Anakin Skywalker of the so-called "Tragedy of Darth Plagueis the Wise", he spoke of the legendary Sith Lord acquiring the power to "influence the midi-chlorians to create life". It is not clear whether or not Palpatine was lying on this occasion.

The Dark Jedi Desann managed to artificially infuse the Force to non Force-sensitive individuals by using special Artusian crystals. Desann referred to these people as the Reborn. Whether his method had anything to do with midi-chlorians remains a mystery, but it is thought that either the crystals caused the midi-chlorians to multiply or somehow 'reinforced' the ones that already existed, producing a totally artificial Force-sensitivity.

Behind the scenes
The concept of midi-chlorians was introduced in Episode I. Some fans of the saga saw midi-chlorians as adding hard science to the mysteriousness of The Force and disliked the new concept.

In real science, midi-chlorians appear to be based on mitochondria, which were once separate organisms that inhabited living cells and have since become part of them. Mitochondria are the power plants of cells, suggesting that perhaps midi-chlorians create the energy of life and thus The Force. Unlike midi-chlorians, which in the Skywalker family are passed on by both father and mother, mitochondrial DNA is only transmitted on the maternal side.

The cause-and-effect relationship between midi-chlorians and Force-sensitivity seems to be a matter of debate. In The Phantom Menace, Qui-Gon Jinn states that users sense the Force through midi-chlorians; however, some argue that he may have been giving Anakin Skywalker a childish explanation, and that the midi-chlorians may actually be a simple indicator rather than the actual method of communication.

Despite how it might first appear, the existence of non-living yet Force-enhancing objects such as rocks and crystals, does not seem to contradict the midi-chlorian explanation. Midi-chlorians are simply a way for organics to perceive the Force, and thus a non-organic object can be strong with the Force without perceiving it, just as a light emitting object does not necessarily have eyes.

The existence of some non-organic beings which are occasionally Force-sensitive (such as the Shards and the Tsil) does pose more of a problem, though an explanation may yet appear.

It is possible that while midi-chlorians provide a way to communicate with the Force, they are not necessarily a measure of Force ability as a whole. This idea is supported by the fact that both Anakin Skywalker and Yoda, the two Jedi with the highest known midi-chlorian counts in the Jedi Order, seem to be the most prone to visions received through the Force; or at least more so than others of similar Force ability (such as Mace Windu).

The Willow April Fool's Day entries of the Databank joke that Midi-chlorians may have originated on the planet Andowyne.

Appearances

 * Tag and Bink: Revenge of the Clone Menace
 * Star Wars Episode I: The Phantom Menace
 * Rather Darkness Visible
 * Medstar II: Jedi Healer
 * Yoda: Dark Rendezvous
 * Star Wars Episode III: Revenge of the Sith
 * The Last of the Jedi: A Tangled Web
 * Star Wars Tales 10 intro