280 PHYSIOLOGICAL CHEMISTRY. 



The quantity of neurokeratin in the nerves and in the different 

 parts of the brain has been carefully determined by KUHNE and 

 CHITTENDEKT. They found 3.16 p. m. in the plexus brachialis, 

 3.12 p. m. in the edge of the cerebellum, 22.434 p. m. in the white 

 substance of the large brain, 25.72-29.02 p. m. in the white sub- 

 stance of the corpus callosum, and 3.27 p. m. in the gray substance 

 of the edge of the large brain (when free as possible from white 

 substance). 



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 01, 0.956-2.016 P0 4 , 0.244-0.796 

 C0 3 , 0.102-0.220 S0 4 , 0.01-0.098 Fe 2 (P0 4 ) 2 , 0.005-0.022 Ca, 0.016- 

 0.072 Mg, 0.58 to 1.778 K, 0.450-1.114 Na. The gray substance 

 yields an alkaline ash, the white an acid ash. 



Appendix. 



The Tissue and Fluids of the Eye. 



The retina contains in all 816-880 p. m. water, 72-102 p. m. 

 proteid bodies myosin, albumin, and mucin (?), 9-32 p. m. lecithin, 

 and 2.7-10.6 p. m. salts (HOPPE-SEYLER and KAHN). The 

 mineral bodies consist of 420 p. m. NagHPO^ and 350 p. m. NaCl. 



Those bodies which form the different segments of the rods 

 have not been closely studied, and the greatest interest is therefore 

 connected with the coloring matters of the retina. 



Visual purple, also called rhodopsin, erythropsin, or VISUAL RED, 

 is the pigment of the rods. BOLL observed in 1876 that the layer 

 of rods in the retina during life had a purplish-red color which 

 was bleached by the action of light. KUHNE showed later that this 

 red color might remain for a long time after the death of the ani- 

 mal if the eye was protected from daylight or investigated by a 

 sodium light. By 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 

 chiefly in the rods and only in their outer parts. In animals whose 

 retina has no rods the visual purple is absent, and is also necessarily 



