100 The Microscope (chap. 9) 



fibrous proteins show less detail. Information can be obtained concern- 

 ing molecular orientation, particle and molecular size and sometimes 

 detailed molecular structure. The image recorded can be related to 

 simple absorption processes and thus be interpreted chemically. 



The simplest method with X-rays is to place a tissue section in con- 

 tact with a fine-gTained photographic emulsion and expose it. Magnifi- 

 cation is obtained in an X-ray projection microscope by separating the 

 sample and film. This requires very fine focusing. One of the principal 

 disadvantages of the method is that vacuum is required; therefore 

 material has to be dry, no water can be present. Freeze-dried tissue can 

 be used. 



USES OF X-RAY 



Tissues with relatively high X-ray absorption are bone and tissues 

 impregnated with heavy metals. The distribution of mineral salts in 

 undecalcified sections of bone can be clearly shown and quantitative 

 information obtained. Substances containing high percentage of ele- 

 ments of high atomic numbers can be injected into blood vessels, or the 

 lymphatic system, and photographed with fine-grain film. Recorded 

 images can be related to simple absorption processes and then be inter- 

 preted chemically. By using the oblique incidence of X-rays, it is 

 possible to determine the thickness of bone tissue or nerves. 



The determination of dry weight (mass) of cellular structures can be 

 made with X-rays, but the interference microscope can also be employed 

 for mass determination. In the latter case, the material can be alive and 

 in fluid. Sometimes it is advantageous to compare both methods as 

 coiuiterchecks on artifacts: is either or are both producing artifacts? — 

 the interference microscope because of fluid being present, or the X-ray 

 product because the material is fixed or dried. 



Ultraviolet Microscopy 



Short waves beyond the visible spectrum have a profound effect upon 

 living matter and are useful for the physical analysis of such matter. 

 Some living material under the influence of ultraviolet radiation visibly 

 radiates, glows and fluoresces. Some does not and remains dark. A 

 microscope for this type of observation has been designed with optical 

 glass in the objectives but is equipped with a quartz substage condenser. 

 A quartz lamp condenser is part of the system to help concentrate the 

 maximum amoiuit of near violet on the specimen. The object itself 

 should not fluoresce, biu will absorb, partially absorb or transmit the 



