An artron inhibitor was a device that inhibited the block-transfer equations that made reconstitution and regeneration of a TARDIS's outer plasmic shell possible, limiting their invulnerability while also draining the artron energy they needed as a power source. As an apparent side-effect, it also disabled the Time Lords' own ability to regenerate. After Simpson was injured falling from a great height, he was unable to regenerate due to the inhibitor's effect. He managed to survive but it took him fifty years to recover.