THE VISUAL PIGMENTS AND THEIR PHOTOPRODUCTS 



recorded within the first minute thereafter ('lumi-rhodopsin'). The 

 film was kept about an hour in darkness, after which its spectrum 

 was again recorded ('meta-rhodopsin'). Finally, the film was soaked 

 in neutral buffer solution for 10 min., and re-dried. Its density 

 spectrum was then measured ('wetted and re-dried*). 



The correspondence between the various stages shown in Figs. 

 2.9 and 2.10 is obvious, and shows that the sequence of changes, first 



zo 40 60 ao 400 zo -oo eo eo ^qO ^° 

 w av s t enq th — rr 



10 60 ao ^00 ^o ^^ ^< 



Fig. 2.10. Bleaching of cattle rhodopsin (visual purple) at room tem- 

 perature in a dry film. Curves give the density spectra of the preparation 

 after the following treatments. 'Rhodopsin,' before bleaching; 'lumi- 

 rhodopsin,' immediately after exposure to a photoflash lamp; 'meta- 

 rhodopsin,' about 1 hr. (in darkness) later; 'wetted and redried,' after 

 soaking in neutral buffer for 10 min. and then redrying — all in darkness. 

 (Wald, Durell and St. George (1950)) 



revealed at low temperatures can equally well be demonstrated at 

 normal temperatures in the absence of water. From this we may infer 

 that the lumi- and meta-rhodopsin stages do exist in bleached visual 

 purple solutions at ordinary temperatures but that they have a very 

 short Hfe. 



It is unUkely that lumi-rhodopsin could survive in solution at 3°C 

 (lythgoe and quilliam*s conditions) long enough to have affected 

 the measurements shown in Fig. 2.7. It seems reasonable, there- 

 fore, to identify lythgoe and quilliam's transient orange with 



49 



