  In CHPT the hadron masses obtain loop corrections from the pseudoscalar
mesons which are identified with the Goldstone bosons of broken chiral
symmetry. An expansion of the baryon mass in the quark masses therefore
includes non-analytic terms. We calculate the nucleon mass in the one-loop
approximation to order $m^4 \sim m_q^2$. We compare the result in the
relativistic and in the heavy mass formulation of the theory and derive
matching relations between corresponding low-energy constants. We calculate the
pion-nucleon loop in old-fashioned perturbation theory and find a contribution
to the $m^4 \ln m$ term from an intermediate state which does not occur in the
heavy baryon theory.
