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Abstract
A model for a micro-crystal of silver bromide in a chemically non-sensitized emulsion is proposed. Each crystal has a sub-structure consisting of a number of polyhedral blocks, slightly misaligned, the boundaries of which form intense local dislocations. The network of dislocations so formed is responsible for the localized separation of silver, and a high density region of dislocations constitutes the sensitivity centre of the crystal. The mechanism of the formation of the latent image is described on this model. Chemical sensitization is then explained by the adsorption of the sensitizer to the more active regions formed by the intersection of the dislocations and the surface of the crystal. Subsequently the sensitizer may spread over the rest of the surface. Its function is to trap the positive holes formed during exposure. Surface and internal latent image, and both high-intensity and low-intensity reciprocity failure are accounted for by this model.