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VISUAL PURPLE. C15
free as possible from white substance). The white is decidedly richer
in neurokeratin than the peripheral nerves or the gray substance. ’
Accord-
ing to Griffiths,1
neurochitin replaces neurokeratin in insects and Crus-
tacea, the quantity of the first being 10.6-12 p. m.
The quantity of mineral constituents in the brain amounts to 2.95-
7.08 p. m. according to Geoghegan. He found in 1000 parts of the
fresh, moist brain 0.43-1.32 CI, 0.956-2.01G P04 ,
0.244-0.796 C03 ,
0.102-0.220 S04 , 0.01-0.098 Fe2 (P04) 2 ,
0.005-0.022 Ca, 0.016-0.072
Mg, 0.58-1.778 K, and 0.450-1.114 Na. The gray substance yields an
alkaline ash, the white an acid ash. Magnus-Levy 2
found in fresh brain
substance 1.305 p. m. CI, 0.166 p. m. Ca, 0.139 p. m. Mg, and 0.083 p.m.
Fe.
Appendix.
THE TISSUES AND FLUIDS OF THE EYE.
The retina contains in all 865-899.9 p. m. water, 57.1-84.5 p. m.
protein bodies—myosin, albumin, and mucin (?), 9.5-28.9 p. m. lecithin,
and 8.2-11.2 p. m. salts (Hoppe-Seyler and Cahn ;;
). The mineral bodies
consist of 422 p. m. Na2 HPC>4 and 352 p. m. NaCl. The retina con-
tains, according to Barbieri,4
also cholesterin but no cerebrosides and in
fact none of the specific constituents of the brain substance.
Those bodies which form the different segments of the rods and cones
have not been closely studied, and the greatest interest is therefore con-
nected with the coloring-matters of the retina.
Visual purple, also called rhodopsin, erythropsin, or visual red, is
the pigment of the rods. Boll,5
in 1876, observed that the layer of rods
in the retina during life had a purplish-red color which was bleached
by the action of light. Kuhne 6 later showed that this red color might
remain for a long time after the death of the animal if the eye was pro-
tected from daylight or investigated by a sodium light. Under these
conditions it was also possible to isolate and closely study this substance.
Visual red (Boll) or visual purple (Kuhne) has become known mainly by
the investigations of Kuhne. The pigment occurs mainly in the rods and only
in their outer parts. In animals whose retina has no rods the visual purple is
^ompt. Rend., 115.
2
Geoghegan, Zeitschr. f. physiol Chem.. 1; Magnus-Levy, Bioch. Zeitschr. 24.
* Zeitschr. f. physiol. Chem., 5.
4
Compt. Rend., 154.
5
Monatsber. d. Kgl. Preuss. Akad., 12. Nov., 1876.
6
The investigations of Kuhne and his pupils, Evvald and Ayres, on the visual purple
will be found in ..Untersuchungen aus dem physiol. Institut der Universitat Heidel-
berg, 1 and 2, and in Zeitschr. f. Biologie, 32.
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