Many cell structures are anisotropic, that is, they transmit ordinary 

 or plane-polarized light at different velocities depending on the direction 

 in which it passes through the structure. For this reason, such structures 

 are said to be birejrigent or double refracting. When ordinary white light 

 is passed through a polarizing element, such as a sheet of Polaroid film. 



Anal yzer 



Polarizer 



Figure 11-22. Schematic Diagram Showing the Alignment of Polarizer 

 and Analyzer When in the Uncrossed (left) and Crossed Positions (right) 

 in the Polarization Microscope. 



it emerges as plane-polarized light oscillating in a single plane perpen- 

 dicular to the direction in which the light is traveling (Figure 11-23). 

 Plane-polarized light produced in this manner, on passing through an 

 anisotropic object, is split into two components which oscillate in mutu- 

 ally perpendicular planes (Figure 11-24). On emerging from the object, 

 the two polarized components are recombined, but as their relative 

 velocities through the object are different, they will be out of phase, i.e., 

 one ray will be retarded relative to the other. In Figure 1 1-24, the ray (S) 



SURVEY OF CYTOLOGICAL TECHNIQUES / 243 



