STUDIES IN SPECIAL SENSE PHYSIOLOGY 369 



We have no direct means of investigating adaptive changes in any 

 animals except man, but we can measure this pupillary response ; 

 if we find it changing in the manner described, it is not an unfair 

 inference to suppose that visual responsiveness may be similarly 

 affected by adaptation. 



It has been found that intensities of red and blue which ap- 

 peared equally bright to and exerted the same pupillo-motor effect 

 upon a human " light " eye, did not produce identical changes 



Triplea: Lamp. 



Slit in Telescope. 

 Separating Prism/. 



Cylinder of Blacked, Paper 56 c.m>. long. 



Gcmvea> Lens. Focal Length/ 10 c.nv. 



(JJL}) Unaccommodated Eye. 

 Fio. 3. AbelsdorfTs apparatus for studying the pupillo-motor response. 



in the pupils of the dove and the owl. For the former the red, 

 for the latter the blue was the stronger stimulus. Indeed the 

 pupillo-motor response to blue in the owl's eye was greater than 

 in the case of a total-colour-blind (Abelsdorff). 



We have now completed a brief review of the experimental 

 facts and are at liberty to consider their importance in our general 

 conception of visual processes. 



First of all, is there any functional difference between the spot 

 of distinctest vision, the fovea centralis retinae, and the paracentral 

 or peripheral regions of the retina ? 



2 A 



