586 BRAIN AND NERVES. 



in cholates is precipitated by saturating with magnesium sulphate, wash- 

 ing the precipitate with a saturated solution of magnesium sulphate, 

 and then dissolving in water by the aid of the cholates simultaneously 

 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, 3 

 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 XVI. 



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 shown 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. r 

 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 342. 



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 membranin 

 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 hydro- 

 chloric acid or ADAMKIEWICZ'S reagent. They are dissolved with great 

 difficulty by pepsin-hydrochloric acid or trypsin solution, but are soluble 

 in dilute acids and alkalies in the warmth. Membranin of the capsule 



1 Kiihne, Zeitschr. f . Biologic, 32. 



2 Kiihne, Die nichtbestandigen Earben der Netzhaut, Untersuch. aus dem physiol. 

 Institut Heidelberg, 1, 341. 



3 Kiihne, ibid., 2, 324. 



4 M6rner, Zeitschr. f. physix)!. 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. 



