Chameleon Arch
From Tardis Wiki, the free Doctor Who reference
The Chameleon Arch was a piece of Gallifreyan equipment which could modify the biology of a creature so the cells were that of something else. The Doctor used it to change himself into the Human John Smith to escape the Family of Blood. (DW: Human Nature) The procedure is verry painful.
The Doctor wearing the Chameleon Arch. From this picture you can see how painful the procedure is
