Ch. VII] PHOTOGRAPHING WITH THE MICROSCOPE 223 



low and moderate power work. And even for 2 mm. homogeneous 

 immersion objectives, the time of exposure is not excessive for many 

 specimens (40 seconds to 3 minutes). This light is cheap and easily 

 obtained. 



A lamp with flat wick about 40 mm. wide has been found most 

 generally serviceable. For large objects and low powers the flame 

 may be made large and the face turned toward the mirror. This 

 win light a large field. For high powers the edge toward the mirror 

 gives an intense light. The ordinary glass chimney answers well, 

 especially where a shield is used (fig. 58). 



In managing the Ught for photography with the microscope, follow 

 the directions given in Ch. II, and under drawing in Ch. VI. See 

 below for the use of color screens. 



§ 346. Objects suitable for photo-micrographs. — While almost 

 any large object may be photographed well with the ordinary camera 

 and photographic objective, only a small part of the objects mounted 

 for microscopic study can be photo-micrographed satisfactorily. 

 Many objects that can be clearly seen by constant focusing with the 

 fine adjustment appear almost without detail on the screen of the 

 photo-micrographic camera and in the photo-micrograph. 



If one examines a series of photo-micrographs the chances are that 

 the greater number will be of diatoms, plant sections, or preparations 

 of insects. That is, they are of objects having sharp details and 

 definite outlines, , so that contrast and definiteness may be readily 

 obtained. Stained microbes also furnish favorable objects when 

 mounted as cover-glass preparations, but these give color images and 

 require a color screen. 



For success with preparations of animal tissue they must approxi- 

 mate as nearly as possible to the conditions more easily obtained with 

 vegetable preparations. That is, they must be made so thin and be 

 so prepared that the cell outUnes have something of the definiteness 

 of vegetable tissue. It is useless to expect to get a clear photograph 

 of a section in which the details are seen with diflSculty when studying 

 it under the microscope in the ordinary way. 



Many sections which are unsatisfactory as wholes may neverthe- 

 less have parts in which the structural details show with satisfactory 



