248 , 



SUBJECTIVE FUNCTIONS OF THE EYE. 



THE word subjective thus used was given by Purkinge 

 (a physicist whom I knew at Breslau) to a class of phe- 

 nomena meriting more attention than they have re- 

 ceived difficult of study, it is true, from their complex 

 and transient nature, and their diversity in different 

 persons. Science has well taught us the modes under 

 which light reaches the retina and optic nerve. But 

 here we lose the traces of it as a physical agent, both 

 as regards the visual perception conveyed to the mind 

 and. those reflex lights and images of which we can 

 hardly define the seat, but which emerge from within 

 the eye, and are the subjects of distinct perception by 

 the mind. 



These spectra vary greatly, and, under different 

 bodily conditions, in the same person. They require 

 to produce them the exclusion, more or less complete, 

 of outward vision ; and pressure upon the eye, either 

 by closure of the lid or some stronger compression 

 from without. I regret not to have made more note of 

 their forms and changes in my own case. But there 

 are two forms which have drawn so strongly upon my 

 attention for some time past, for the last year espe- 

 cially, that I think them worthy of notice among these 

 curious phenomena. 



