CRYSTALLINE LENS. 617 



Visual purple must always be prepared exclusively in a sodium light. It is 

 extracted from the net membrane by means of a watery solution of crystallized 

 bile. The filtered solution is evaporated in vacuo or dialyzed until the visual 

 purple is separated. To prepare a visual-purple solution perfectly free from 

 haemoglobin, the solution of visual purple in cholates is precipitated by saturating 

 with magnesium sulphate, washing the precipitate with a saturated solution of 

 magnesium sulphate, and then dissolving in water by the aid of the cholates sim- 

 ultaneously precipitated. 1 



The Pigments of the Cones. In the inner segments of the cones of birds, rep- 

 tiles, and fishes a small fat-globule of varying color is found. KUHNE 2 has 

 isolated from this fat a green, a yellow, and a red pigment called respectively 

 chlorophan, xanthophan, and rhodophan. 



The dark pigment of the epithelium-cells of the net membrane, which was 

 formerly called melanin, but has since been named fuscin by KUHNE and MAYS,* 

 contains iron, dissolves in concentrated caustic alkalies or concentrated sul- 

 phuric acid on warming, but, like the melanins in general, has been little studied. 

 The pigment occurring in the pigment-cells of the choroid will be discussed with 

 the melanins in Chapter XV. 



The vitreous humor is often considered as a variety of gelatinous 

 tissue. The membrane consists, according to C. MORNER, of a gelatin- 

 forming substance. The fluid contains a little proteid and a mucoid, 

 hyalomucoid, which was first show T n by MORNER, and which is precipitated 

 by acetic acid. This contains 12.27 per cent N, and 1.19 per cent S. 

 Among the extractives we find a little urea according to PICARD 5 p. m., 

 according to RAHLMANN 0.64 p. m. PAUTz 4 found besides some urea, 

 paralactic acid, and, in confirmation of the claims of CHABBAS, JESNER, 

 and KUHN, also glucose in the vitreous humor of oxen. The reaction 

 of the vitreous humor is alkaline, and the quantity of solids amounts 

 to about 9-11 p. m. The quantity of mineral bodies is about 6-9 p. m., 

 and the proteins 0.7 p. m. In regard to the aqueous humor see page 

 361. 



The Crystalline Lens. That substance which forms the capsule of 

 the lens has been investigated by C. MORNER. It belongs, according 

 to him, to a special group of proteins, called membranins. The mem- 

 branin bodies are insoluble at the ordinary temperature in water, salt 

 solutions, dilute acids, and alkalies, and, like the mucins, yield a reducing 

 substance on boiling with dilute mineral acids. They contain lead- 

 blackening sulphur. The membranins are colored a very beautiful red 

 by MILLON'S reagent, but give no characteristic reaction with concentrated 

 hydrochloric acid or ADAMKIEWICZ'S reagent. They are dissolved with 



1 Kuhne, Zeitschr. f . Biologic, 32. 



2 Kuhne, Die nichtbestandigen Farben der Netzhaut, Untersuch. aus dem physiol. 

 Institut Heidelberg, 1, 341. 



3 Kuhne, ibid., 2, 324. 



4 Morner, Zeitschr. f. physiol. Chem., 18; Picard, cited from Gamgee, Physiol. 

 Chem., 1, 454; Rahlmann, Maly's Jahresber., 6; Pautz, Zeitschr. f. Biologic, 31. A 

 complete review of the literature will also be found here. 



