The passage discusses the use of photobleaching techniques in studying molecular movement within cell membranes and the cytoplasm. It highlights that about 25% of bungarotoxin-acetylcholine receptor complexes were immobile during photobleaching measurements, suggesting that the ligand o-bungarotoxin may reduce the lateral mobility of the receptor. The technique has been applied to study actin polymerization and the diffusion of macromolecules in living cells, showing that the cytoplasmic matrix can hinder the free diffusion of such molecules. These applications suggest that photobleaching can provide unique dynamic information on cellular structures when interpreted with biochemical and ultrastructural data. The second part of the passage focuses on the discovery of multiple imaging of quasars due to gravitational lenses. It mentions three confirmed examples and the detection of a gravitational lens responsible for one of these images. The phenomenon is interpreted unambiguously, with the optical emission line spectra of different images being identical. The general properties of gravitational lenses are explained, and three papers in the Astrophysical Journal explore speculative suggestions involving gravitational lenses. These include the idea that quasars may be amplified by intervening lenses, the potential perturbation of quasar statistics by lens amplification, and the possibility of multiple imaging by a gravitational lens in a cluster of quasars at a high redshift. The papers discuss the challenges and limitations of these models, emphasizing the need for further research to confirm these findings.The passage discusses the use of photobleaching techniques in studying molecular movement within cell membranes and the cytoplasm. It highlights that about 25% of bungarotoxin-acetylcholine receptor complexes were immobile during photobleaching measurements, suggesting that the ligand o-bungarotoxin may reduce the lateral mobility of the receptor. The technique has been applied to study actin polymerization and the diffusion of macromolecules in living cells, showing that the cytoplasmic matrix can hinder the free diffusion of such molecules. These applications suggest that photobleaching can provide unique dynamic information on cellular structures when interpreted with biochemical and ultrastructural data. The second part of the passage focuses on the discovery of multiple imaging of quasars due to gravitational lenses. It mentions three confirmed examples and the detection of a gravitational lens responsible for one of these images. The phenomenon is interpreted unambiguously, with the optical emission line spectra of different images being identical. The general properties of gravitational lenses are explained, and three papers in the Astrophysical Journal explore speculative suggestions involving gravitational lenses. These include the idea that quasars may be amplified by intervening lenses, the potential perturbation of quasar statistics by lens amplification, and the possibility of multiple imaging by a gravitational lens in a cluster of quasars at a high redshift. The papers discuss the challenges and limitations of these models, emphasizing the need for further research to confirm these findings.