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This paper reviews the experimental and theoretical work on photographic sensitivity and related topics which has been published during the past ten years. New experimental results, obtained to a large extent with model systems, have necessitated substantial revision and amplification of previously accepted theories. The role of crystal imperfections in all aspects of photographic sensitivity is now recognized and emphasis has shifted from the trapping of electrons, which characterized the Gurney-Mott theory, to the trapping of positive holes. The latent image consists of small groups of silver atoms formed by the combination of silver ions and electrons. This proceeds through intermediate stages in which first latent pre-image and then latent sub-image specks appear. The initiation of development by latent image specks of different sizes is discussed in the final sections. The approach which is followed in this paper leads to an integrated treatment of the whole range of photographic phenomena in which very few hypotheses with no direct experimental foundation have to be introduced.
J. W. Mitchell (Tue,) studied this question.