180 THE USE OF THE MICROSCOPE 



Care of the Object Traverser (Detachable Mechanical 



Stage). — This useful piece of apparatus only requires ordi- 

 nary care to keep balsam, immersion oil, acetic acid, etc., 

 out of the rackwork, and free from the stage. The up-and- 

 down motion must be kept tighter than the transverse 

 movement. 



Care of the Objectives. — These are the most important 

 parts of the microscope. They must not be let fall, or the 

 balsam in their compound lenses may be sprung. Hence 

 they are best kept screwed on the nosepiece. The writer 

 has seen cases where the balsam in the lenses was melted 

 and caused to bubble by excessive heat, perhaps from too 

 close proximity to the lamp. It is said that the front lens 

 of an immersion objective is readily broken (Spitta). It 

 is usually fastened in place by a thin flange of metal turned 

 over the edge of the glass, which oil will not pass. This 

 is not the case, however, with some oil-immersion objec- 

 tives of 1.4 aperture, where the front lens is held only by a 

 thin line of cement which will not stand alcohol. The 

 front lens of a dry objective must be kept optically clean. 

 One touch with the clean finger will cause a fingerprint, 

 which will dull the image. Even touching the sheet of 

 lens paper with the clean fingers will prevent perfect polish- 

 ing. The writer polishes first with lens paper moistened 

 with distilled water, and then with a small roll of dry lens 

 paper, using the end of the roll only, and tearing off a fresh 

 surface each time. The back of an objective should be 

 kept free from dust, by blowing off any that settles there. 

 It can be cleaned, if necessary, by a roll of lens paper 

 wrapped round filter paper, after breathing on it, or mois- 

 tening it with distilled water. A water-immersion objec- 

 tive, in the writer's experience, requires the front lens to be 

 cleaned from grease, by the occasional application of lens 

 paper moistened with xylol. Only distilled water should 

 be used in cleaning lenses. 



The oil should not be allowed to dry on an oil-immersion 

 objective; but should be cleaned ofT first with lens paper, 

 or filter paper, then with lens paper moistened with xylol. 



