X rays. Photograhic emulsions are suspensions of silver halide crystals 

 in gelatin. As a result of exposure to light or ionizing radiation (e.g., 

 X rays), the silver bromide crystals are reduced to metallic silver (black) 

 by photographic development. The resultant negative can be examined 

 and rephotographed at higher magnifications by means of the conven- 

 tional optical microscope (Figure 11-31). 



In projection microradiography, the photographic film is moved back 

 from contact with the specimen. This results in enlargement of the 

 shadow produced by the X rays passing through the specimen and falling 

 on the photographic emulsion (Figure 11-30). The principle of projec- 

 tion microradiography is utilized in the construction of the compound 



Figure 11-31. Contact Radiograph of Transverse Section of Human 

 Bone. (From Kirkpatrick, P. and Pattee, H. H., Jr., 1953. '"Approaches to 

 X-Ray Microscopy," in Lawrence, J. H. and Tobias, C. A. (Eds.), Advances 

 in Biol. Med. Physics, 3, Academic Press Inc., New York, N. Y.. Fie. 1, 

 p. 249.) 



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