  This is a self-contained pedagogical review of Polchinski's 1986 analysis
from first principles of the Polyakov path integral based on Hawking's zeta
function regularization technique for scale-invariant computations in
two-dimensional quantum gravity, an approach that can be adapted to any of the
perturbative string theories. In particular, we point out the physical
significance of preserving both Weyl and global diffeomorphism invariance while
taking the low energy field theory limit of scattering amplitudes in an open
and closed string theory, giving a brief discussion of some physics
applications. We review the path integral computation of the pointlike
off-shell closed bosonic string propagator due to Cohen, Moore, Nelson, and
Polchinski. The extension of their methodology to the case of the macroscopic
loop propagator in an embedding flat spacetime geometry has been given by
Chaudhuri, Chen, and Novak. We examine the macroscopic loop amplitude from the
perspective of both the target spacetime massive type II supergravity theory,
and the boundary state formalism of the worldsheet conformal field theory,
clarifying the precise evidence it provides for a Dirichlet (-2)brane, an
identification made by Chaudhuri. The appendices contain extensive detail.
