CH. Ill] CARE OF THE MICROSCOPE 93 



The field should be lighted well and the aperture of the objective filled about 

 f full of light. If there are any defects as smears of balsam or liquids on 

 the front lens, unsealing of the combinations, or dust on the upper face of the 

 back lens the defect can be seen in the eye-point. 



Another and very certain method of detecting imperfections is to rotate the 

 different elements while looking into the microscope. If the defect is in the 

 mirror they will change in position when the mirror is moved, and so with all 

 the other elements. Defects in the ocular are strikingly shown by rotating it. 



158. Lens paper. The so-called Japanese filter paper, which, 

 from its use with the microscope, I have designated lens paper, has 

 been used in the author's laboratory since 1884 for cleaning the lenses 

 of oculars and objectives, and especially for removing the fluid used 

 with immersion objectives. Whenever a piece is used once it is thrown 

 away. It has proved more satisfactory than cloth or chamois, be- 

 cause dust or sand is not present; and from its bibulous character it 

 is very efficient in removing liquid or semi-liquid substances. 



159. Removal of dust, etc. (i) Dust may be removed with 

 a camel's hair brush, or by wiping with the lens paper. 



(2) Cloudiness may be removed from the glass surfaces by breath- 

 ing on them, then wiping quickly with a soft cloth or the lens 

 paper. 



Cloudiness on the inner surfaces of the ocular lenses may be removed 

 by unscrewing them and wiping as directed above. A high objective 

 should never be taken apart by an inexperienced person. 



If the cloudiness cannot be removed as directed above, moisten 

 one corner of the cloth or paper with 95% alcohol, wipe the glass first 

 with this, then with the dry cloth or the paper. 



(3) Water may be removed with soft cloth or the lens paper. 



(4) Glycerin may be removed with cloth or lens paper saturated 

 with distilled water; remove the water as above. 



(5) Blood or other albuminous material may be removed while 

 fresh, the same as glycerin. If the material has dried on the glass, it 

 may be removed more readily by adding a small quantity of ammonia 

 to the water in which the cloth is moistened (water 100 c.c., ammonia 



I C.C.). 



(6) Canada Balsam, damar, paraffin, or any oily substance may 

 be removed with a cloth or paper wet with chloroform, gasoline or 

 xylene. The application of these liquids and their removal with a 



