606 



Jagendorf and Hind 



(5^0 mu) with itself, so light scattering artefacts 

 were implicated. On a split beam instrument it was 

 apparent that actinic light caused an increase in optical 

 density of the suspension. -^'his can even be seen in a 

 Carey spectrophotometer; representative tracings are 

 shown in Fig, 3« 



LIGHT-INDUCED OPTICAL DENSITY INCREASE 



pH6 -PYO 



pH6 +PYO 



3H8 +PYO 



Figure 3. Optical density at 5^0 mu as a function of 

 actinic illumination with red light (660 mu and up). 

 25 ugm of chlorophyll in a total volume of 3 nil, 

 containing NaCl 10 mM, 3,3-diraethylglutaric acid and 

 iris at 20 mM, pH 6.0 or 8.0 as shown. Pyocyanine at 

 .05 mM. Temperature approximately 5 C, measurements in 

 Carey model 1^ with simultaneous illumination from above, 

 using microscope illumination lamp filtered through 

 Corning heat filter and Kodak Wratten Gelatin filter 

 no. 70, 



The changes is very non-specific for wavelength, occurring 

 from the ultraviolet to 730 mu, at least. In addition 

 the extent of the change is minimized upon using opal 

 glass cuvettes, and maximized by using additional narrow 

 slits before the photomultiplier (l4). All of these 



