In fact, the theatre has been a conservative influence, tending to oppose innovation and to maintain the integrity of the form of tragedy. The essentials of its literary form, its length conditioned by the time of the performance, the division into acts, scenes, or parts, and the growing importance of dialogue, have all been dependent on theatrical conditions. The characteristic qualities of national dramas have been in some measure the products of the national theatres, and only through the growing similarity of stage conditions are we likely to attain agreement in regard to the forms of drama. While there have been a multitude of tragedies that have never been acted, and some that have never been intended for acting, the attempt to write tragedy for the closet rather than for the stage has resulted either in adopting the supposed conditions of the Greek or some other foreign theatre, or in breaking away from the strict limits defined by the stage and writing lyrical medleys or dramatic monologues or imaginary conversations. As soon as tragedy has left the theatre, it has reverted to old forms or developed new and strange hybrids. Milton's "Samson Agonistes" and Swinburne's "Bothwell" are tragedies, if you will, but they have no place in the development of a national drama. Shelley's "Prometheus Unbound," Browning's "The Ring and the Book," and Landor's "Marcellus and Hannibal" are all dramatic, but they cannot be included in any definition of the species of tragedy. Object as tragedy rightly may at times to the limitations and trivialities of the theatre, it cannot safely leave its precincts without losing its own identity. In the past nearly all tragedies of any effect on the drama's development have not only been planned for the stage but have succeeded when acted. This seems likely to be the case in the future. For the reader of a play is confronted by difficulties not found in other fiction; and, in general, only a play suited to presentation on the stage is likely to secure for a reader the visualization, the impersonations, the illusion of actuality, similar to those experienced in the theatre. The fact that the drama requires the services of theatre and actors as well as author need not lessen our recognition of the responsibility and opportunities of the one or the other. The stage affords the first test of a play's emotional appeal, and perhaps the best test of its dramatic power. The consummation of tragedy has been attained only when the dramatist has availed himself of all the aids that the theatre has offered.