The first clinical definition appears in Copland's "Dictionary of Practical Medicine" in editions between 1833 and 1858. Later Strauss (1950) defines it as "the inability to perform the sexual act". Ernest Jones (1918) declares it is "the complete or incomplete inability satisfactorily to carry out heterosexual coitus per vaginam. Satisfactorily means adequate erection, time and control of ejaculation."