The Kinetics of Dark Adaptation

1. Purpose.--Many photosensitive animals acquire in the dark an increased sensibility to light. A quantitative description of this process of dark adaptation is limited, however, to very few animals. For vertebrates, there are the numerous and accurate measurements with man (Piper, 1903; Nagel, 1911; Hecht, 1921-22); the few observations with the chick (Honigmann, 1921); and the measurements with the tadpole (Obreshkove, 1921); while for invertebrates there are only the data with the clam, Mya arenaria (Hecht, 1918-19 b). Additions to this meager collection of data are obviously desirable. The first purpose of the present paper is to present measurements of the dark adaptation of two additional invertebrates: the lamellibranch, Pholas dactylus; and the ascidian, Ciona intestinalis. The original study of the dark adaptation of Mya (Hecht, 1918-19 b) contained an analysis of the process in terms of a photosensory mechanism. Since then, much has been learned about the nature of the processes involved, and as a result certain modifications in the details of the theoretical treatment have become necessary (Hecht, 1922-23). The second purpose of this paper is to present an analysis of the data of dark adaptation which is in keeping with present knowledge.