In 1934 Bok argued that the observed phenomenon of clustering of galaxies could not be caused by intergalactic dust matter distributed like the interstellar clouds of dust in the Milky Way. Bok considered background clusters between foreground clusters of galaxies, while Zwicky investigated distant concentrations of galaxies through foreground clusters. Regarding the most distant chains of galaxies observed in the blue band, we investigate the foreground obscuration caused by dust. We indicate the case that galaxies between long chains of galaxies may be considered as obscured by solid grains, familiar of early investigations in statistical astronomy; probably the extinction law is similar to interstellar extinction. We agree with Zwicky's view that intergalactic matter affects the clustering of galaxies: moreover, we extend his research programme to the space between clusters of galaxies. Contrary to half-century tradition, the large clouds of grains similar to the grains occurring in the atmosphere of some stars must be taken as a real factor in the coil of complicated problems connected with the clustering of galaxies.