  We generalize the Jackiw-Rebbi-Hasenfratz-'t Hooft construction of fermions
from bosons to demonstrate the fermionic nature of certain bound states
involving SU(N) instantons in even spatial dimensions and SO(N) instantons in
$8k+1$ spatial dimensions. We use this result to identify several fermionic
excitations in various perturbatively bosonic string theories. In some examples
we are able to identify these fermions as excitations in known conformal field
theories and independently confirm their fermionic nature. Examples of the
fermions we find include certain 3-string junctions in type 0B theory,
excitations of the 0-p system in type 0A theory, excitations of the stable
D-particle of type O theory, and a rich spectrum of fermions in the bosonic
string compactified on the SO(32) group lattice.
