612 RADIATION BIOLOGY 



by light) for the most part acted Hke pure on-elements, responding most 

 readily to the onset of cathodal stimulation. A minority of these, how- 

 ever, gave a readier on-response to anodal stimulation. One generaliza- 

 tion, applicable to the electrical stimulation of any on-off -element, was 

 that on- and-off-responses \\ere elicited by opposite directions of current. 

 The authors suggest, on the basis of these experiments, that the on- and 

 off-components are unrelated; that on-components arise from rods, 

 whereas off-components arise from cones; and that the various compo- 

 nents are tied in with the "element" by means of direct and indirect 

 neural paths, including horizontal and amacrine cells of the retina. 

 They also consider that on-responses are simple and direct, whereas 

 off-responses indicate the predominance of an inhibitory process based 

 on the horizontal or associational neurones. 



Electrical polarization has also been studied for its effects upon the 

 responsiveness of retinal elements to stimulation by light. Gernandt 

 (1947) reports that pure on-elements and most of the cathodal on-off- 

 elements are little affected by polarization. Other on-off-elements and 

 off-elements are markedly affected, however, and the on- and off-compo- 

 nents may be quite independently altered by the presence of the polariz- 

 ing current. Specifically, spectral sensitivity was studied in the presence 

 of electrical polarization. The results on the retinal elements of cats 

 bear some resemblance to the findings of Kravkov and Galochkina on 

 changes in spectral sensitivity produced by polarization in the human 

 eye. Cathodal and anodal polarization, for example, were shown to have 

 opposite effects upon the thresholds for stimulation by spectral lights. 

 Although this principle holds for all the basic types of element (on-, off-, 

 and on-off-elements), it is the on-off-elements that again are of greatest 

 interest. For them it is found that the on- and off-components are differ- 

 entially affected by polarization. The most common spectral locations 

 for marked changes in threshold due to polarization were found to lie at 

 470, 520, 570, and 600 mn. The changes at 600 m/i are particularly 

 noticeable. Furthermore it is often found that the on- and off-compo- 

 nents of the same element are found in "contrasting" regions of the 

 spectrum. 



These observations are typical of those made by Granit and his 

 coworkers on the effects of polarization upon sensitivity to light. The 

 interpretation that these authors give is as follows: On-elements behave 

 like visual rods in being relatively more sensitive to short wave lengths 

 of light. Their responsiveness is fairly independent of horizontal con- 

 duction paths and hence httle affected by electrical polarization. Off-ele- 

 ments and on-off-elements, on the other hand, have partly photopic 

 characteristics. Their responsiveness is much influenced by horizontal 

 conduction and hence by electrical polarization. The coexistence of 

 on- and off-components within the same retinal element, often affected 



