Literary Notices. clxxiii 



termini are figured from the ciliary body. Somewhat similar termini 

 are figured in the iris, together with an intricately meshed terminal 

 plexus superficially. 



The previous observation that the circular and radial muscular 

 fibres freely anastomose is verified and the interesting fact is added that 

 the same motor fibre often divides so as to supply one end organ to a 

 radial and another to a circular fibre. The musculature of the iris, 

 then, like that of the ciliary body, both as regards its structure and its 

 innervation, must be regarded as a single, rather than a double 

 mechanism. 



The Significance of the Optic Purple in Vision. 1 



Some of the author's more important conclusions are given in the 

 seven theses below. For the detailed observations and experiments 

 from which these conclusions are derived we must refer the reader to 

 the original paper. 



i. In the fovea centralis (and all cones) no optic purple occurs. 



2. The uncolored sensation (gray) generally called forth at the 

 threshold of the stimulus (with the exception of the red) is occasioned 

 by a feeble decomposition of the optic purple. 



3. By stronger decomposition of the optic purple, up to the 

 point where the optic yellow is first formed, the sensation of blue is 

 called forth. 



4. The two still -unknown optic substances for the two other 

 fundamental sensations red and green are (like the optic yellow) more 

 difficult of decomposition than the optic purple. 



It follows from 1 and 3 that the fovea is blue-blind ; trichromatic 

 persons have here a dichromatic color system and dichromatic persons 

 a monochromatic color system. This area has in the authors' right 

 eye an apparent diameter of 55 to 70 minutes of arc, which is thus 

 larger than the angle subtended by the moon. Viewing the moon 

 through blue glass the author succeeded after long practice in holding 

 the gaze steady enough to cause the disc to disappear entirely when 

 fixed in the fovea. The sensation is not that of looking into empty 

 space formerly occupied by the moon, but as if the gaze were fixed 

 close beside the latter. A sort of vicarious point of fixation seems to 

 have been established. 



1 Koenig, A. Ueber den menschlichen Sehpurpur und seine Bedeutung 

 fur das Sehen. Math, und naturw. Mitth. Sitsb. Akad. der IViss. zu Berlin, 

 Heft 6, 1894. 



