COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 67 



INTERPRETATION OF RESULTS, 



How are our results to be explained? Can they be brought into 

 line with any or all of the theories of color-vision now in the field ? Can 

 they contribute to an evaluation of the relative merits of the rival 

 theories ? 



Any attempt to express our results in terms of physiological process 

 reveals the possibility of four general principles of interpretation: 

 (i) It may be held that the phenomena which have been found to be 

 characteristic of indirect vision are wholly due to the peculiar objective 

 conditions which must, from the nature of the case, attend the stimula- 

 tion of the peripheral retina. (2) On the other hand, it may be held that 

 these phenomena are the result of a peculiarity of structure or of chemi- 

 cal composition of the peripheral retina. (3) It may be conceived that 

 the phenomena in question are to be referred to a simultaneous co- 

 operation of the factors mentioned under i and 2. And (4) all of 

 these views may be discarded as inadequate ; one may conclude, instead, 

 that the phenomena in question can not be explained in terms of a 

 modification of retinal process at all, and conceive that they are to be 

 referred to a cerebral or other central process whose nature it is im- 

 possible to envisage or describe. 



(i) The first view either conceives the retinal surface to be uniform 

 in structure and composition throughout its whole area, or regards 

 those differences which may be held to occur as being of negligible sig- 

 nificance. It refers the transitions of color-tone to the physical form 

 of the visual organ, and the spatial arrangement of its parts, emphasiz- 

 ing the fact that the retinal surface occupies such a position relative to 

 that of the pupil and of the lens, that its outlying parts possess less 

 favorable conditions for vision than its central region. The advocate 

 of this view need not assume that the color-sensing substance with 

 which the periphery is supplied is in any wise different from that which 

 is found at the center. For the defective refraction of oblique rays of 

 light, and the non-perpendicular position of the plane of the pupil to 

 that of the path of the incident light naturally and necessarily give rise 

 to a less bright and less well-defined peripheral image. In short, a 

 given pencil of rays constitutes a lesser physiological stimulus in indi- 

 rect than in direct vision, for the simple reason that in the former a part 

 of the light fails to gain access to the pupil, while the part which does 

 enter is imperfectly focused upon the retina. 



This view as here formulated has perhaps never been advocated by 

 any single writer ; but it is a composite statement of the positions held 

 by Albini on the one hand, and on the other by a group of investigators 



