  The generalized Weierstrass representation for surfaces in $\Bbb{R}^{3}$ is
used to study quantum effects for strings governed by Polyakov-Nambu-Goto
action. Correlators of primary fields are calculated exactly in one-loop
approximation for the pure extrinsic Polyakov action. Geometrical meaning of
infrared singularity is discussed. The Nambu-Goto and spontaneous curvature
actions are treated perturbatively.
