The Third Doctor only said the full phrase "reverse the polarity of the neutron flow" twice on screen – in "The Sea Devils" (1972) and the 20th Anniversary special "The Five Doctors" (1983). Pertwee used the phrase when he acted in the stage play "Doctor Who – The Ultimate Adventure" in 1989. When Colin Baker took over the role in the play he amended the line to "Reverse the linearity of the proton flow." In the radio play "The Paradise of Death", the Brigadier asks "Reverse the polarity of the neutron flow?" and the Doctor proceeds to explain that the phrase is meaningless (neutrons are chargeless, so to reverse the polarity of a neutron flow is to do nothing at all). On other occasions on screen, the Third Doctor "reversed the polarity" but not of neutrons.