THE HOMOGENEITY OF VISUAL PIGMENT SOLUTIONS 



P2, in admixture are shown graphically. Each curve refers, as indi- 

 cated, to a given photosensitivity ratio (determined by the wave- 

 length of the bleaching hght). When the ratio is unity it is impossible, 

 of course, to achieve any separation by bleaching. This is shown in 

 Fig. 6.5 by the line, marked '1:1,' having equal ordinate and abscissa 

 values. For other ratios, separation is possible to a greater or less 

 degree. The whole family of curves, some of which are drawn in 

 Fig. 6.5, is symmetrical about the line '1:1.' Thus the curve labelled 

 *100: r is the counterpart of that labelled *1 : 100,' and so on. 



SOME RESULTS OBTAINED BY PARTIAL 

 BLEACHING 



A BINARY MIXTURE 



In a recent investigation bridges (1955) found that visual pigment 

 solutions prepared from rainbow trout {Salmo irideus) were not 

 homogeneous. On exposing the solutions to monochromatic Hght 

 of long wavelength bleaching was, at first, maximal at about 532 mfx. 

 As bleaching continued, however, the Amax of the difference spectra 

 obtained shifted to shorter and shorter wavelengths. After prolonged 

 exposure to the long- wave bleaching light, only about one-half of the 

 total photosensitive material was bleached. The less-sensitive residue 

 was readily bleached, however, by employing a bleaching hght of 

 short wavelength. 



The results of one of the partial bleaching experiments are set out 

 in the following table. 



Bleaching conditions 



1. 35 min, X = 650 m^ 



2. 35 min, X = 650 mfji 



3. 14 hr, X = 670 mfx 



4. 35 min, X = 650 m// 



5. 25 min, X = 580 ruju 



6. 10 min, white light 



From these, and other similar experiments, bridges concluded 

 that the rainbow trout solutions contained a mixture of two photo- 

 sensitive pigments : one with Xmax at 533 m^, and apparently 

 identical with the visual pigment 533 of tench, pike and bleak 

 (d ARTN ALL, 1 952a, 1 955) the other with Amax at 507 m^ and similar to, 

 if not identical with, the visual pigment 5 10 of bleak. It was relatively 



169 



