BRAIN AND NERVES. 281 



absent in the macula lutea. In a variety of bat (rliinoloplius hip- 

 posideros), in hens, pigeons, and new-born rabbits, no visual purple 

 has been found in the rods. 



A solution of visual purple in water which contains 2-5# 

 crystallized bile, the best solvent for it, is purple-red in color, quite 

 clear, and not fluorescent. On evaporating this solution in vacua, we 

 obtain a residue similar to ammonium carminate which contains 

 violet or black grains. If the above solution is dialyzed with water, 

 the bile is diffused and the visual purple separates as a violet mass. 

 Under all circumstances, even when still in the retina, the visual 

 purple is quickly bleached by direct sunlight, and with diffused 

 light with a rapidity corresponding to the intensity of the light. It 

 passes from red and orange to yellow. Ked light bleaches the 

 visual purple slowly; the ultra-red light does not bleach it at all. 

 A solution of visual purple shows no special absorption-bands, but 

 only a general absorption which extends from the red side, beginning 

 at Z>, to the line G. The strongest absorption is found at K 



Visual purple when heated to 52-53 C. is destroyed after several 

 hours, and almost instantly when heated to +76 C. It is also 

 destroyed by alkalies, acids, alcohol, ether, and chloroform. On the 

 contrary, it resists the action of ammonia or alum solution. 



As the visual purple is easily destroyed by light, it must there- 

 fore also be regenerated during life. KUHISTE has also found that 

 the retina of the eye of the frog becomes bleached when exposed for 

 a long time to strong sunlight, and that its color gradually returns 

 when the animal is placed in the dark. This regeneration of the 

 visual purple is a function of the living cells in the layer of the 

 pigment epithelium of the retina. This may be inferred from the 

 fact that a detached piece of the retina which has been bleached 

 by light may have its visual purple restored if the detached piece 

 of the retina be carefully laid on the chorioi'dea having layers of the 

 pigment epithelium attached. The regeneration has, it seems, 

 nothing to do with the dark pigment, the melanin or fuscin, in the 

 epithelium cells. A partial regeneration seems, according to 

 KUHNE, to be possible in the completely-removed retina. On ac- 

 count of this property of the visual purple of being bleached by 

 light during life, we may, as KUHNE has shown, under special con- 

 ditions and by observing special precautions, obtain after death by 



