  We calculate the expectation values of the energy-momentum tensor
T_{{\mu}{\nu}} for massive scalar and spinor fields, in the Minkowski-like
vacuum states on the two flat spaces which are quotients of Minkowski space
under the discrete isometries (t,x,y,z)\mapsto(t,x,y,z+2a) and
(t,x,y,z)\mapsto(t,-x,-y,z+a).
  The results on the first space confirm the literature.
  The results on the second space are new. We note some qualitative differences
between the massless and massive fields in the limits of large a and large
x^2+y^2.
