INFRA-RED AND ULTRA-VIOLET MICROSCOPY 241 



A fluorescent specimen may be examined either in transmitted 

 or reflected light. In the former case, the layout is that of a standard 

 microscope. A filter is set in front of the condenser so that the specimen 

 is irradiated only with the radiation required. Frequently, uUra-violet 

 radiation, extending over a wide wave-length range, can be selected 

 and, then, all that is required is a filter eliminating the visible spectrum. 

 A second filter, set in the microscope proper, lets through the visible 

 fluorescent light but occludes the ultra-violet. 



In reflective examinations, various arrangements may be used: 

 those of Lieberkuhn (Fig. 4.17), of Chapman and AUdridge (Fig. 4.18), 

 mirror objectives and so forth. When low magnifying powers are 

 involved and the distance between the objective and the specimen is 

 adequate, illumination can be efl'ected laterally, using an illuminator 

 not integral with the microscope. Lastly, to secure valuable information 

 regarding the details observed, it may be desirable to study the 

 spectral constitution of the fluorescence generated. Such is the object 

 of microspectroscopic fluorescence the fundamentals of which are 

 set forth in Chapter X. 



