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Molecular Basis of Vision /1 9 : 4 



Retinene 2 is also a mono-cis compound, but the location of the cis bond 

 has not been determined. 



A list of some of the known pigments of this general type is given in 

 the accompanying table. 



Pigment 



TABLE I 



Absorption 

 maximum 



m^u, Carotenoid Protein 



Source 



retinene 2 



Birds and reptiles have mostly cones in their retinas and probably 

 lack rods. These cones contain bright colored oil globules between the 

 inner and outer cone segments. These oils are all carotenoids. Wald 

 extracted 1,600 bird eyes to isolate the following oils 



Color vision is clearly possible with just these filters and iodopsin. 



4. The Origin of the Neural Spike 



Many experiments indicate that one photon dissociates one retinene! 

 group from one rod opsin molecule. It is completely unknown how 

 one or two such dissociations can give rise to a neural spike. This is 

 one of the most fundamental questions which may be asked about the 

 molecular changes in vision. One suggestion is that somehow the 



