460 CHROMOPHANES. [BOOK I. 



ether and doubtless similar to, if not identical with, those extracted by 

 these solvents from the nervous tissues. Kiihne has found, indeed, that 

 the contents of the outer limbs behave to osmic acid in almost the 

 same manner as the medullary sheath of nerves ; to the substance in 

 the contents which exhibits this reaction Kiihne ascribes the name 

 of rod-myeloid (Stabchen-myeloid), though he does not wish thereby 

 to indicate that it is a definite proximate principle. 



Solubility -^ ax Schultze first pointed out, and his observations 



of the outer are confirmed by Kiihne, that the contents of the 

 limbs of both outer limbs of the rods and cones are dissolved with 

 rods and extraordinary rapidity and ease by bile, the envelope 



cones imbue. alone remaining 



Colouring matters associated with cones. (Chromophanes?) 



The outer limbs of the cones differ from those of the rods in being 

 invariably free from colouring matters. In birds, reptiles and fishes, 

 however, the inner segment of each cone presents a minute globular 

 body, apparently of a fatty nature, and possessed of brilliant and 

 varied colours, violet, blue, green, yellow, and red, though red and 

 yellow are most frequently met with. 



The fact that the pigments are held in solution by fats is proved 

 by the intensely brown colour which the coloured globules acquire 

 when treated with perosmic acid and by the fact that they are 

 dissolved by such solvents of fatty bodies as a mixture of alcohol and 

 ether, carbon disulphide, and benzol. 



Whilst the colouring matters of the cones are grouped together 

 under the name of Chromophanes, Kiihne 1 has succeeded in separa- 

 ting, and examining the physical properties of, three distinct colouring 

 matters, a green, a yellow, and a red, which he distinguishes by the 

 names of chlorophane, xanthopJiane and rhodophane respectively. 



Method of A large number of eyes (50 to 300) of doves or hens 



separating are bisected so as to cut off the anterior segments ; the 

 the Chromo- vitreous humor being removed, the posterior segments 

 of the eyes are placed at once in absolute alcohol ; as 

 soon as possible the alcohol is poured away and the eyes are tho- 

 roughly exhausted with ether. On evaporating the ether, a fiery-red" 

 fat is obtained which is dissolved in hot alcohol and saponified by the 

 action of caustic soda, water being used to replace the alcohol as it 

 evaporates. The hard soap which separates from the mother liquor 

 is well dried and then treated successively with petroleum ether, then 

 with ether, lastly with benzol, which dissolve in order Chlorophane, 

 Xanihophane, and Khodophane ; for the methods of purification the 

 reader is referred to the original paper. 



General All the chromophanes when treated with solution of 



characters of iodine assume, as Schwalbe pointed out, a blue colour 



the chromo- which differs in intensity and shade according to the 



phanes. shade of the particular chromophane. The chromo- 



1 Kiihne und Ayres, Ueber lichtcbestdndige Farben der Netzhaut. 



