PHASE-CONTRAST MICROSCOPY 



89 



Phase-contrast microscopes in ultra-violet and infra-red radiations 



Discounting construction problems, the phase-contrast method is 

 applicable to the ultra-violet and infra-red radiations just as it is to 

 the visual range. Yet it should be noted that transparent objects 

 in the visual range may become absorbent in the ultra-violet and 



Fio. 2.24. Selection of organism including the rosette Oscillospira, Guilliermondii, sarcina, 



Quin's organism and selenomas. Ultra-violet negative phase-contrast. J. Smiles and 



M. J. Dobson (courtesy of Cooke, Troughton and Simms). 



infra-red radiations. This apphes to many biological specimens: in 

 ultra-violet light some parts of living cells are absorbent and, when 

 phase-contrast imaged, are more tricky to interpret. The imaged 

 contrast is the outcome of incident radiations absorbed by the sub- 

 stance and a phase-contrast effect. These two effects are not necessarily 

 additive: let us consider a shghtly-contrasted non-dephasing detail 

 in ultra-violet radiation. Applying phase contrast converts low-con- 

 trast, non-dephasing objects into transparent ones. 



