The Force: A Detailed Explanation
Part 2 - The Link to the Force
The Greater and the Lesser Force are inherently linked, and may thus interact with and affect one another. Their interaction leaves a "footprint" trace in the form of mysterious living particles in the blood known as Midi-chlorians. These Midi-chlorian traces also serve to facilitate and enhance further communication between the Greater and Lesser Force.
In ancient times it was held by many that Midi-chlorians were not distinct entities, but rays of the Greater Force Itself. This view is still held by many Jedi.