48 LABORATORY GUIDE IN BACTERIOLOGY 



adjustment pillar. The fine adjustment consists of 

 a delicate screw-thread, which is easily damaged. 



3 . The lenses, condenser, and mirror, when necessary, 

 should be wiped with Japanese lens paper, never with 

 any coarse material. 



4. For cleaning use a damp cloth. For wiping the 

 lenses use water or xylol. Never use alcohol, as this' 

 dissolves the cement holding the lenses in place and 

 also injures the lacquer. 



5. Do not take the instrument apart. The working 

 parts are of delicate nature and easily injured. Be 

 careful not to drop the oculars or objectives. 



6. The incUnation joint can be used only with dry 

 lenses and dry objects, not with the oil-immersion or 

 hanging-drop preparations. 



7. After placing the object on the stage, focus with 

 a low power and the coarse adjustment. With high 

 powers use the coarse adjustment first and the fine 

 adjustment afterward. The free use of the fine adjust- 

 ment saves the accommodation of the eye. As the 

 eye is capable of accommodating itself to distances, it 

 may, with an effort, distinguish a picture which is not 

 in perfect focus. This effort is saved by using the 

 fine adjustment. 



8. Raise the draw tube by means of the coarse 

 adjustment before changing the objectives or examin- 

 ing a different preparation. 



9. Before focusing, obtain as good light as possible 

 by turning the mirror, and then regulate the supply 

 by the diaphragm. Always use reflected light, never 

 direct sunlight. 



10. When focusing an object, lower the draw tube 

 until the lens almost touches the cover glass. This 



