  The spectrum of massless bosonic and fermionic fluids satisfying the equation
of state $p=(\gamma-1)\rho$ is derived using elementary statistical methods. As
a limiting case, the Lorentz invariant spectrum of the vacuum ($\gamma=0,
p=-\rho$) is deduced. These results are in agreement with our earlier
derivation for bosons using thermodynamics and semiclassical considerations.
