THE VISUAL PIGMENTS 



was very rapid and consequently only a rough estimate could be 

 obtained. 



Fig. 2.7 shows the results of one experiment. After measuring 

 the density spectrum of the visual purple solution (V.P.) it was 

 exposed for 3 sec. to a very intense hght. Optical density measure- 

 ments within the wavelength ranges of 460-490 mju and 395-430 m^ 



450 



Wavelength m rrifj 



Fig. 2.7. The density spectrum of transient orange (T.O.) in relation to 

 that of the parent (frog) visual purple (V.P.). The numbers against the 

 points give the times (in seconds) at which the readings were taken, and 

 the arrows show the order of taking them. The curve I.Y. was measured 

 when the thermal decomposition of transient orange was complete. 

 3°C, pH7-13. 

 {Lythgoe and Quilliam, 1938) 



were then made as quickly as possible. The numbers in Fig. 2.7 give 

 the times (seconds from end of exposure) at which the relevant 

 measurements were made. After readings had been repeated for 

 about I hr. the temperature of the solution was raised to c. 20°C for 

 20 min. in order to complete the thermal destruction of the transient 

 orange. The solution was then cooled again and it yielded the curve 

 lY in Fig. 2.2. The readings on the curve TO in Fig. 2.7 were all 

 taken within Ijmin. after bleaching and give the approximate 



44 



