  The Glauber method is extensively used to describe the motion of a hadronic
projectile in interaction with the surrounding nuclear medium. One of the main
approximations consists in the linearization of the wave equation for the
interacting particle. We have studied the consequences of such an assumption in
the case of the $^{12}\mathrm{C(e,e}'\mathrm{p)}^{11}\hbox{\rm B}^*$ reaction
at high proton momenta by comparing the results with the predictions obtained
when all the ingredients of the calculation are unchanged but the second-order
differential equation for the scattered wave, which is solved exactly for each
partial wave up to a maximum of 120 spherical harmonics. We find that the
Glauber cross section is always larger by a factor $10 \div 20 \%$, even at
vanishing missing momenta. We give a quantum-mechanical explanation of this
discrepancy. Nevertheless, a good correlation is found between the two
predictions as functions of the missing momentum, especially in parallel
kinematics.
