CHEMICAL BASIS OF THE ANIMAL BODY. 1313 



pigment is obtained are more especially abundant in the frog. 

 It is soluble in chloroform, ether, benzene, carbon-sulphide, etc. 

 When dissolved in ether it gives two absorption bands between 

 F and Gr; in carbon-bisulphide two bands, one each side of F. 

 The pigment of the body-fat of frogs gives similar absorption 

 spectra when dissolved in the same solvents. Solutions of 

 lipochrin are slowly bleached by exposure to a strong light. 

 The pigment is probably closely allied to the yellow colouring- 

 matter of many other animal fats. 



3. Chromophanes. 



These are the colouring substances of the red, green and 

 yellow fat-globules which occur in the outer end of the inner 

 limbs of the retinal cones. They are prepared, as yet, chiefly 

 from the eyes of birds, as follows. The retinas are dehydrated 

 with alcohol and extracted with ether. The ethereal solution 

 of the fats is then evaporated to dryness, the residue dissolved 

 in hot alcohol and saponified with caustic soda. The hard 

 coloured soaps thus obtained are then extracted in succession 

 with petroleum ether (see note p. 1272), ether and benzene: of 

 these solvents the first dissolves out the yellowish-green chloro- 

 phane, the second the yellow xanthophane and the third the 

 red-coloured rhodophane. 



(i) Chlorophane. Soluble in petroleum ether, ether, car- 

 bon-bisulphide and in alcohol. When dissolved in the first 

 two of these solvents it shews two absorption bands between 

 F and G- ; in solution in the latter, the two bands lie one each 

 side of F. 



(ii) Xanthophane. Soluble in ether, carbon-bisulphide 

 and in alcohol. In ethereal solution it shews only one absorp- 

 tion band near F towards the blue end of the spectrum. In 

 carbon-bisulphide it shews similarly one band near, and to the 

 blue side of b. It is thus distinguished from the yellow pig- 

 ment (lipochrin) of the retinal epithelium previously described. 



(iii) Rhodophane. Soluble in turpentine, benzene and in 

 alcohol. In benzolic solution it shews one band close to, but 

 on the red side of F; in solution in turpentine the band is 

 similarly near, but now on the blue side of F. 



Solutions of the chromophanes are slowly bleached by the 

 action of light, chlorophane losing its colour fairly rapidly, 

 xanthophane more slowly and rhodophane only after prolonged 

 exposure. 



4. Visual-purple (Rhodopsiri). 



Its distribution in the retina has been sufficiently described 

 in § 576. 



Preparation in solution. The most suitable material is 



83 



