CH. II] LIGHTING AND FOCUSING. 57 



CARE OF THE MICROSCOPE. 



§ 104. The microscope should be handled carefully and kept perfect- 

 ly clean. The oculars and objectives should never be allowed to fall. 



When not in use keep it in a place as free as possible from dust. 



All parts of the microscope should be kept free from liquids, especial- 

 ly from acids, alkalies, alcohol, benzin, turpentine and chloroform. 



§105. Care of the Mechanical Parts.— To clean the mechanical 

 parts put a small quantity of some fine oil (olive oil or liquid vaselin 

 and benzin, equal parts), on a piece of chamois leather or on the lens 

 paper, and rub the parts well, then with a clean dry piece of the cha- 

 mois or paper wipe off most of the oil. If the mechanical parts are 

 kept clean in this way a lubricator is rarely needed. Where opposed 

 brass surfaces "cut," i. e., when from the introduction of some gritty 

 material, minute grooves are worn in the opposing surfaces, giving a 

 harsh movement, the opposing parts should be separated, carefully 

 cleaned as described above and any ridges or prominences scraped down 

 with a knife. Where the tendency to " cut " is marked, a very slight 

 application of equal parts of beeswax and tallow, well melted together, 

 serves a good purpose. 



In cleaning lacquered parts, benzin alone answers well, but it should 

 be quickly wiped off with a clean piece of the lens paper. Do not use 

 alcohol as it dissolves the lacquer. 



§ 106. Care of the Optical Parts. — These must be kept scrupu- 

 lously clean in order that the best results may be obtained. 



Glass surfaces should never be touched with the fingers, for that will 

 soil them. 



The glass of which the lenses are made is quite soft, consequently it 

 is necessary that only soft, clean cloths or paper be used in wiping them. 



Whenever an objective is left in position on a microscope, or when 

 several are attached by means of a revolving nose-piece, an ocular 

 should be left in the upper end of the tube to prevent dust from falling 

 down upon the back-lens of the objective. 



§ 107. 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 for the last ten years 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, because 

 dust and sand are not present ; and from its bibulous character it is very 

 efficient in removing liquid or semi-liquid substances. 



