A theoretical analysis is made of the spontaneous emission from an excited atom or a molecule in a one-dimensional periodic structure formed by a screened two-conductor line filled with periodically distributed dielectric disks. It is shown that when the transition frequency lies within or close to the forbidden band of the periodic structure, the decay of an excited state of an atom or a molecule produces a characteristic long-lived dynamic state. This dynamic state is a superposition of the excited and ground states with an admixture of a photon "cloud," which surrounds the atom or molecule. A study is made of the distribution of the electromagnetic energy of the dynamic state. The energy and the decay law of the excited state are obtained and the spectrum of the emission which accompanies this decay is obtained. It is shown that the spontaneous emission can be suppressed strongly in volumes much greater than the wavelength. The possibility of the suppression of spontaneous emission from lasers is discussed.