"In 1911 [Martinez Sierra and his wife/co-author Maria] achieved a definitive and permanent triumph with the production of The Cradle Song.... The Cradle Song is a reminiscence of Maria's youth in Carabanchel, a town in which her father was convent doctor and where her sister took the veil, the Sister Joanna of the Cross of the play. [Martinez] has paused to probe some universal passion or emotion... in The Cradle Song, to echo the cry of the eternal mother instinct while has been stifled ...