The fog centers on primitive silver bromide emulsion grains (mainly tabular) which have not been exposed to light were ovserved by electlon microscope and analysed some proparties of these centers. The dispersity, size or location of the fog centers produced by the surface-developer depends on the concentration of developing agent; in the development by glycine-carbonate surface-developer of Stevens' original formula, numerous fog centers were produced. These centers were formed preferentially

more »

... n the central region of flat surface of large grains. These centers were not observed to grow in size, but instead many new fog centers weregradually formed during prolonged developing. In the development by a diluted surface-developer solution, a few fog centers were formed. Preferred formation of these centers on the central region of grain surface was not observed in this case. Prolonged development caused the growth of these fog centers, which resulted in filamentary form. This is contrary to the case with the above-mentioned concentrated developer (Stevens' original formula).