The ultraviolet microscope can be adapted for use as a spectropho- 

 tometer to measure changes in the absorption of nucleic acids and 

 proteins in cell structures. This method has been used to study metabolic 

 changes during cell division, growth, and differentiation (Figure 1 1-20). 



i 



Photoelectric cell 

 image 



Amplifier I A 

 Galvanometer ( o 



i\ ,' 



Quartz 

 ocular 



>-- 



Ultraviolet 

 ligtit source 



4) 



Quartz 



monochromotor 



central 



> 





Quartz 

 objective 



iQuartz slide 



and cover strip 

 Quartz condenser 



beam 



/^ Quartz 

 ^ reflector 



Figure 11-21. Schematic Diagram Showing Light Source, Monochro- 

 mator. Microscope, and Photoelectric Apparatus for Measuring the Absorp- 

 tion of Ultraviolet Light by Cell Structures. (From Gersh, I. and Bodian, 

 D., 1943. "Some Chemical Mechanisms in Chromatolysis," /. Cell. Comp. 

 Physiol, 21, Fig. 1, p. 257.) 



When operated in this manner, the specific absorption of the substance 

 under study is usually recorded by a photoelectric cell mounted above 

 the body tube of the microscope (Figure 11-21). Briefly, the method 

 involves splitting a monochromatic beam of ultraviolet light into two 

 beams, one of which falls directly on a photoelectric cell (the "blank") 



SURVEY OF CYTOLOGICAL TECHNIQUES / 241 



