ELECTRICAL PHENOMENA IN VISION 



583 



historical review of the research in this field. Fortunately Granit's book 

 (1947) and reviews (1950a, b) are available for a detailed summary of his 

 voluminous work and the related work of other investigators. The book 

 by Bartley (1941), the thorough review of the early literature by Kohl- 

 rausch (1931), and the later review by Graham (1934) may also be con- 

 sulted for more comprehensive treatments of these topics. 



THE RESTING POTENTIAL 



Every eye appears to exhibit a relatively large (several millivolts) and 

 constant "resting potential." In the case of vertebrates the cornea is 

 normally found to be positive with respect to the fundus, but for inverte- 

 brates the polarity is reversed. Vertebrates have "inverted" retinas in 



100 



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z 

 o 



Q. 



W 



60 



(a) 



40 



< 20 





 -10 





12 3 4 5 6 7 



POSITION ON EYE 



(b) 

 Fig. 13-2. Distribution of the resting potential around the eyeball, (a) The indiffer- 

 ent electrode is at position 1 at the fundus of the eye. [b) The various magnitudes of 

 constant potential recorded between this electrode and an active one at each of the 

 designated points are plotted in the graph. {Redrawn from Kohlrausch, 1931.) 



the sense that the rods and cones are pointed away from the light, whereas 

 invertebrate receptor cells point toward the light. Hence we may state 

 the general finding that the constant polarity of any eye is such that the 

 terminal portions of the receptor cells are usually found to be negative 

 in relation to the basal portions. 



Many observations support the view that the resting potential of the 

 eyeball originates primarily in the retina. Whether the sensory cells are 

 responsible for it is not known, nor can we be sure that some small part 

 of the resting effect is not extraretinal in origin. Some of the relevant 

 observations are the following: Early experimenters [e.g., Holmgren, 

 Dewar, and McKendrick (see Granit, 1947)] claimed to find a resting 

 potential in isolated retinas. Others [especially de Haas, Westerlund 

 (see Kohlrausch, 1931)] studied the distribution of the resting potential 

 around the eyeball (see Fig. 13-2). They found maximal potential dif- 

 ferences between leads on the cornea and fundus. Relatively large dif- 

 ferences were found betw^een adjacent regions in the anterior portion of 



