Data on the absorption by a crystalline powder of Ge and on the intensities diffracted by the (111) planes of a perfect Ge crystal were collected in the laboratory at frequencies of the incident X-ray beam close to the photoelectric resonance for theK electrons of Ge. A high-resolution, double-crystal spectrometer with the two crystals in the dispersive position was used to obtain the data. The real part of the dispersion contribution to the atomic-scattering factor was calculated from the experimental absorption data by using the Kramers-Kronig relation. The (111) diffracted intensities were also calculated and compared to the experimental ones. The agreement is good up to an incident beam frequency which is ≈1.5 eV below the resonant frequency. Then the two curves deviate, and the calculated curve is well below the experimental one. It is suggested that this disagreement is due to a quantum effect, similar to the «cavity quantum electrodynamics» effect observed in the microwave and visible frequency range. This effect should be due to the interaction of the dynamical diffraction with the dispersion phenomenon.