1 9 5 7 , ▁he ▁was ▁appointed ▁Reg ius ▁Professor ▁of ▁Phys ic , ▁succeed ing ▁Sir ▁Lion el ▁Whit by . ▁In ▁ 1 9 5 8 , ▁he ▁gave ▁the ▁Dun ham ▁L ect ures ▁at ▁Harvard ▁University . ▁He ▁o vers aw ▁the ▁expansion ▁of ▁medical ▁teaching ▁at ▁Cambridge , ▁including ▁the ▁introduction ▁of ▁two ▁new ▁ch airs ; ▁Professor ▁of ▁Medicine ▁in ▁ 1 9 6 3 ▁and ▁Professor ▁of ▁S urg ery ▁in ▁ 1 9 6 5 . ▁He ▁also ▁o vers aw ▁the ▁development ▁of ▁the ▁new ▁School ▁of ▁C lin ical ▁Medicine . ▁In ▁ 1 9 7 5 , ▁he ▁stepped ▁down ▁from ▁the ▁Reg ius ▁Professor ship ▁and ▁returned ▁to ▁his ▁previous ▁appointment ▁of ▁Professor ▁of ▁Rad i other ape ut ics . ▁ ▁He ▁retired ▁from ▁academ ia ▁and ▁clin ical ▁medicine ▁in ▁ 1 9 7 6 . ▁ ▁Personal ▁life ▁In ▁ 1 9 3 4 , ▁Mitchell ▁married ▁L ilian ▁Mary ▁Bu xt on ▁who ▁was ▁eight ▁years ▁his ▁senior . ▁together ▁they ▁had ▁two ▁children ; ▁a ▁son ▁and ▁a ▁daughter . ▁His ▁wife ▁prede ce ased ▁him ▁in ▁ 1 9 8 3 ▁but ▁he ▁was ▁surv ived ▁by ▁his ▁children . ▁ ▁In ▁ret irement ▁he ▁continued ▁to ▁live ▁in ▁Cambridge ▁in ▁a ▁house ▁on ▁Hun ting don ▁Road . ▁He ▁died ▁on ▁ 2 2 ▁February ▁ 1 9 8 7 ▁in ▁Cambridge . ▁ ▁Hon ours ▁In ▁ 1 9 5 2 ,