90 PROGRESS IN MICROSCOPY 



The works published related to phase-contrast in ultra-violet and 

 infra-red radiation are few: Bennett, Woernley and Kavanagh, in the 

 USA, Taylor in England, have described and used phase-contrast 

 microscopes in ultra-violet radiation. Barer has constructed an infra- 

 red device comprising an electron image converter. Figure 2.24 shows 

 a photograph made with the ultra-violet phase-contrast microscope 

 designed by Cooke, Troughton and Simms. 



7. PHASE-CONTRAST APPLICATIONS 



Phase-contrast apphcations in the various branches of Science and 

 Industry are manifold. Only a few such applications are briefly out- 

 Hnes herein. 



In cytology, phase-contrast microscopy permits observation of cells, 

 tissue fragments and histological-preparation sections. Cell nuclei and 

 protoplasmic structures are positively identified. Ludin showed that 

 phase-contrast microscopes show chiefly the cell nucleus and membrane 

 whereas staining methods evidence the chromatin structure. 



Extensive phase-contrast research has been made in connection 

 with the cytoplasmic structure, mitochondria, fibropiast spindles, the 

 Golgi apparatus, living ceUs and so forth. 



Albertini made extensive research with phase-contrast microscopes 

 to investigate and diagnose tumours. 



In haematology, extended observation of blood and medulla cells 

 was made by means of phase-contrast microscopy. 



It should be noted that Zernike's method applies equally well to 

 animal and plant cytology. Research pertaining to the cells of algae 

 and metaphysical plants has been carried out, too. 



Phase-contrast microscopy has also provided valuable results in 

 the study of parasitic worms (egg growth), in diagnosing dermato- 

 mycosis in mycology and observation /// vivo of bacteria. 



Particularly useful applications of phase-contrast microscopy are 

 those in the fields of chemistry, crystallography and mineralogy. 

 Colourless crystals having an index different from that of the medium 

 encompassing them are typical objects for phase-contrast microscope 

 study. For example, the phase-contrast definition of paraffin micro- 

 crystals in alcohol excels that of polarized light. The latter process 

 only shows the crystal edges whereas in phase-contrast work they 

 appear as thin strips evincing hexagonal symmetry (Bennett). Phase- 

 contrast microscopy is particularly suitable for some crystal-growth 



