CH. II} LIGHTING AND FOCUSING 59 



Fig. 59. Screen for shading the microscope and 

 the face of the observer. This is very readily con- 

 structed as shown in the figure by supporting a wire 

 in a disc of lead, iron, or heavy wood. The screen is 

 then completed by hanging over the bent'wire, cloth or 

 manilla paper 30 x 40 cm. The lower edge of the 

 screen should be a little below the stage of the micro- 

 scope and the upper edge high enough to screen the- 

 eyes of the observer. 



§ 109. Shading the Object.— To get the 

 clearest image of an object no light should 

 reach the eye except from the object. A hand- 

 kerchief or a dark cloth wound around the 



objective will serve the purpose. Often the proper effect may be ob- 

 tained by simply shading the top of the stage with the hand or with a 

 piece of bristol board. Unless one has a very favorable light the shading 

 of the object is of the greatest advantage, especially with homogeneous 

 immersion objectives. The screen (Fig. 59) is the most satisfactory 

 means for this purpose, as the entire microscope above the illuminating 

 apparatus is shaded. 



§ no. Cleaning Homogeneous Objectives. — After one is 

 through with a homogeneous objective, it should be carefully cleaned as 

 follows : Wipe off the homogeneous liquid with a piece of the lens 

 paper (§ 114), then if the fluid is cedar oil, wet one corner of a fresh 

 piece in benzin or chloroform and wipe the front lens with it. Imme- 

 diately afterward wipe with a dry part of the paper. The cover-glass 

 of the preparation can be cleaned in the same way. If the homogen- 

 eous liquid is a glycerin mixture proceed as above, but use water to 

 remove the last traces of glycerin. 



CARE OF THE MICROSCOPE 



§111. The microscope should be handled carefully and kept per- 

 fectly 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, 

 especially from acids, alkalies, alcohol, benzin, turpentine and 

 chloroform. 



§ 112. Care of the Mechanical Parts. — To clean the mechan- 

 ical parts put a small quantity of some fine oil (olive oil or liquid vas- 



