  The string susceptibility exponents of dynamically triangulated 2-dimensional
surfaces with various topologies, such as a sphere, torus and double-torus,
were calculated by the grand-canonical Monte Carlo method. These simulations
were made for surfaces coupled to $d$-Ising spins ($d$=0,1,2,3,5). In each
simulation the area of surface was constrained to within 1000 to 3000 of
triangles, while maintaining the detailed-balance condition. The numerical
results show excellent agreement with theoretical predictions as long as $d
\leq 2$.
