X-RAY MICROSCOPY 



the work of Lamarque, Turchini (83) and 

 others. 



It is necessary to mention here attempts 

 to use for microradiography another ma- 

 terial sensitive to x-rays. W. A. Ladd and 

 M. W. Ladd (80) and Pattee et al. (95) 

 found that a completely grainless x-ray 

 image can be obtained on some plastic (e.g., 

 vinylidene chloride) after a certain exposure 

 time. Although its range of contrasts may 

 be increased through bathing the exposed 

 plastic in NH4OH (10%) the image obtained 

 remains very indistinct. Authors express 

 hope, however, that they will succeed in 

 improving these preliminary results. 



Limit of magnification of microradiograph. 

 It is obvious from the foregoing that the re- 

 solving power of a microradiograph depends 

 upon three components: qualitative and 

 geometrical resolutions by the x-rays, and 

 resolution by the emulsion. Only then can 

 one expect the maximum resolution in a 

 microradiograph when each of these com- 

 ponents produces, in harmony with the 

 others, the best effect. Both qualitative and 

 geometric resolutions are to some extent 

 under the control of the researcher, but the 

 resolution of the emulsion is not. 



Summarizing the data discussed above 

 one may conclude that the maximum mag- 

 nification can be obtained if the microradio- 



, o 



graph IS made: (1) with x-rays 1 A or longer, 

 (2) of a section 10 n and thinner and (3) on 

 fine-grain emulsion like 649-0 or GH sample. 

 This maximum is around 300-336 X, i.e., 

 20 X objective and 15 X eyepiece or 42 X 

 objective and 8X eyepiece. As was men- 

 tioned above the average (working) magnifi- 

 cation is around 120 X to 150 X. Since the 

 average thickness of sections used in micro- 

 radiography is 10 ju, 5 M size is the smallest 

 microstructure of which a sharp and contrast 

 image may be expected. Only in the excep- 

 tional case of a finest-grain emulsion may 

 one observe a sharp and contrast image of 

 detail 1 ju size, but this is possible only in 

 microradiographs of sections 1 to 2 /x thick. 



Apparently one cannot expect notable 

 improvement of the above mentioned limit 

 of magnification in microradiographs for the 

 near future unless a new sensitive material 

 to x-rays will become available. 



One may consider that the little magnifi- 

 cation possible in microradiography cannot 

 reveal new data unknown to general micro- 

 morphology. This is wrong, as will be shown 

 later, because microstructures are seen from 

 a new and peculiar point of view which is 

 presented due to selective x-ray absorption. 

 After all, knowledge of micromorphology is 

 not so perfect that this new possibility may 

 be rejected. 



One may conclude that both contrast and 

 sharpness of contact microradiographs can 

 be obtained sufficient for visualization of 

 micromorphological structures within the 

 limits of the method. These data can be used 

 with certain reservations for qualitative and 

 quantitative analyses of biological tissues. 



Selective X-ray Coloring of Vessels, 

 Canals, Cavities, and other Elements 

 of Biological Tissues 



After Baker, who proposed to use the term 

 "coloring" instead of "staining" in histology, 

 it was thought that the term "x-ray color- 

 ing" could well designate any procedure con- 

 nected with the artificial increase of x-ray 

 absorbing capacities. 



Numerous x-ray coloring media (called 

 here also x-ray opaque or contrast media, or 

 simply OM or CM) are used in microradiog- 

 raphy. Choice depends on the purpose of the 

 research. Negative contrasting (through the 

 injection of air) is not used in microradiog- 

 raphy. Opaque media for microradiography 

 may be introduced either in vivo ("vital 

 injection") or post mortem. The introduc- 

 tion post mortem may be carried out in both 

 humans and animals; vital injection is used 

 only in experiments. There are two kinds of 

 vital injection used in microradiography: 

 (1) direct and (2) indirect. The direct method 

 is called microvasography or microradio- 



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