  We calculate the imaginary parts of the isoscalar scalar and isovector
electromagnetic form factors of the nucleon up to two-loop order in chiral
perturbation theory. Particular attention is paid on the correct behavior of Im
$\sigma_N(t)$ and Im $G_{E,M}^V(t)$ at the two-pion threshold $t_0=4 m_\pi^2$
in connection with the non-relativistic 1/M-expansion. We recover the
well-known strong enhancement near threshold originating from the nearby
anomalous singularity at $t_c = 4m_\pi^2-m_\pi^4/M^2 = 3.98 m_\pi^2$. In the
case of the scalar spectral function Im $\sigma_N(t)$ one finds a significant
improvement in comparison to the lowest order one-loop result. Higher order
$\pi\pi$-rescattering effects are however still necessary to close a remaining
20%-gap to the empirical scalar spectral function. The isovector electric and
magnetic spectral functions Im $G_{E,M}^V(t)$ get additionally enhanced near
threshold by the two-pion-loop contributions. After supplementing their
two-loop results by a phenomenological $\rho$-meson exchange term one can
reproduce the empirical isovector electric and magnetic spectral functions
fairly well.
