ADDING COLOR CONTRAST TO PHASE CONTRAST 



185 



counting, and the phase system revealed smaller particles than could be 

 seen by brightficld methods (see Section 2 of Chapter VI). 



Dispersion has been important to mineralogists and used by them 

 for many years, but only recently has it been explored and recommended 



m 



•**ns 



0.14A-X/4 





V^lx^ * %*'J 



.«» 



>*^ 











i 



Fig. IV.4. Wheat chromosomes stained with acetocarmine, 400 X. A, brightfield. 



B, dark-contrast (A — ) phase. C, high bright-contrast phase. D, same as C, plus 



red filter. Preparation courtesy of Professor Luther Smith. 



for general application with transparent materials (Crossmon, 1948, 

 1949a). For many specimens Crossmon recommends a medium of 

 suitable dispersion, with a refractive index differing from that of the 

 specimen by about 0.004 (see Table V.l). He recommended a darkfield 

 microscope to bring out the details of the specimen in color, but the same 

 method may be even better with the phase microscope, because any 



