OTHER METHODS OF STUDYING VISUAL PIGMENTS 



lower part of the figure are shown the additional changes when the 

 bleaching was completed by white Hght. The total changes on bleach- 

 ing were always the same (within experimental error) whether the 

 retinae were bleached by a single exposure to white hght or first 

 partly bleached with coloured light and then with white hght. 



Blue followed 

 by white 



I I I I I I I 



450 



500 550 600 



Wavelength (m/i) 



650 



Fig. 7.9. Difference spectra of the density changes caused in albino 



guinea pigs' retinae by (A) parti? 1 bleaching by blue light, and (B) further 



bleaching to completion by white light. 



{Weale, 1955) 



These experiments suggest that the guinea-pig retina contains 

 photosensitive pigments in addition to visual purple, but it is not 

 possible, as yet, to unravel the absorption characteristics of the 

 additional pigments. 



RESULTS WITH MAN 



Results which have been obtained with human subjects (camp- 

 bell and RUSHTON, 1954; rushton and Campbell, 1954; rush- 

 ton, CAMPBELL, HAGINS and BRINDLEY, 1955) are separately 



201 



