  Subject of this thesis is the study of a closed bosonic string: the treatment
will follow an approach alternative with respect to the traditional one and
stems from a research line pursued in by Eguchi. A description of the dynamics
using Nonstandard Analysis is given in chapter 10 with prerequisites in
appendices B and C. Detailed calculation are carried out explicitly, although
many of them are deferred to appendix A.
  Selected parts of this thesis have been published as separate articles by the
author<EMAIL_ADDRESS>and collaborators.
