, Microscopes 33 



face of the stage (at right angles to the direction of vision through the 

 microscope), they appear as bright specks due to their reflection of light, 

 but do not show their outline or shape. The apparatus used for such 

 study is called an ultramicroscope (L. ultra, beyond). 



In an ultraviolet microscope invisible ultraviolet rays (of shorter wave 

 lengths and beyond the visible violet light waves) are used instead of 

 ordinary light. Because of the invisibility of the ultraviolet rays, photo- 

 graphs must be made since the image cannot be seen. Special quartz 

 lenses must be employed which permit the passage of the ultraviolet rays. 



Fig. 6. — Correct position when using a microscope. The microscope should 

 stand upright on the table directly in front of the observer. The left hand should 

 be used on the fine adjustment to maintain the proper focus, thus leaving the 

 right hand for other work while looking through the eyepiece. Both eyes should 

 be kept open in order to minimize eyestrain. This microscope has three objectives 

 on the nosepiece and a mechanical stage to move the slide on the stage. (From 

 Carter: Microbiology and Pathology, The C. V. Mosby Co.) 



In dark-field microscopy the term dark field refers to a method of 

 illuminating a specimen brightly while the surrounding background 

 (field) remains dark. The most practical dark field is obtained by a 



