Derivation of the Virasoro Conditions in the String Model

It is shown that the Virasoro conditions and the trajectory equation in the dual resonance model can be derived from the Lagrange coordinate condition in the Nambu-Susskind string model. The proof is based on a causality requirement concerning the vibrational waves on the string and on a lagrangian theory of the free relativistic string with the ordinary time parameter. The case of interaction with an external scalar field is also discussed.