36 COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



magnitude, his results will turn out to be regular and uniform, pro- 

 vided, of course, he is careful to maintain a uniform degree of retinal 

 adaptation throughout his experimentation. There is here no neces- 

 sity for an accurate equalization of stimuli. Hence the factors which 

 he is required to take into account and to control, are at once few in 

 number, relatively simple in character, and easily handled. And it is 

 doubtless to this fact of lesser liability to error of method that the gen- 

 eral agreement in the results of the various investigators of the first 

 problem is due. These results may be summarized in the following 

 general statement: All colors tend to assume a yellowish or a bluish 

 tint as they approach the periphery ; yellow and blue do not themselves 

 change in tone, but the less refrangible end of the spectrum the reds, 

 the oranges, and the greens together with the more reddish purples, 

 appear more and more yellowish as they recede from the visual axis ; 

 while the more refrangible end of the spectrum the violets together 

 with the violetish purples, pass over into bluish or even blue, at but a 

 slight distance from the fovea. To this bald statement of the facts of 

 indirect vision, every investigator with the exception of Schelske, 

 Klug, and Hellpach could subscribe with a clear conscience. The 

 following propositions have also been maintained: The saturations of 

 all color stimuli appear to diminish gradually and steadily, from trn 

 fovea to the outer limits of vision; in addition to the yellow and the 

 blue, a certain tone of red and a certain tone of green undergo no 

 change of color in indirect vision. The first of these propositions is in 

 accord with the observations of the majority of investigators; some, 

 however, make no mention of the phenomenon of decreasing saturation. 

 The second proposition is a product of only the most recent literature ; 

 it has, however, been confirmed in several instances, and has never 

 been called in question by any investigator whose work bears evidence 

 of a knowledge of the precautions to be observed in accurate experi- 

 mentation. 



(2) A similar degree of unanimity is, unfortunately, not to be 

 found in the results of the investigations which have sought to deter- 

 mine where, in passing out over the retina, the changes of color appear. 

 Nor is the reason far to seek. The degree of eccentricity at which the 

 transition of tone will occur, in any given case, is a product, not of one, 

 but of several contributing factors. Numerous investigators have estab- 

 lished the fact that this degree of eccentricity varies with variations 

 in the color tone, in the saturation, in the brightness, and in the area 

 of the stimulus employed, and with changes of optic refraction and of 

 retinal adaptation as well. Since the investigator of this problem must 



