The Microscope. 36t 



is wrinkled the unequal pressure will certainiy break the fragile 

 things. Take the cover between the two folds of the cloth and 

 between the thumb and finger, and gently rub it while it is 

 steadied with the left hand. When one side has been polished, 

 turn it over and repeat the performance. 



Many mechanical devices have been devised and recom- 

 mended for this purpose, but, except with the very thinnest 

 glass they are not necessary. The simplest and most useful of 

 these is made of two flat wooden blocks, with a surface tightly 

 covered with thick, soft chamois skin fastened on with tacks 

 around the sides and where they cannot come in contact with 

 the glass. A cover is placed on the chamois skin and the soft 

 chamois skin surface of the other block placed above it, when 

 the glass is rubbed between them, and so cleaned. When one 

 side is polished, turn the blocks over and clean the other side 

 by the same movements. With this simple apparatus it is 

 hardly possible to break the thinest of covers. If the rubbing 

 leaves them imperfectly polished the application of a little 

 saliva will have a good effect. Some microscopists place their 

 covers in water and sulpliuric acid, washing them afterward in 

 pure water and wiping on a soft rag. This is seldom neces- 

 sary. Sulphuric acid and water should be mixed with exceed- 

 ingly great caution, as so much heat is generated suddenly that 

 disastrous results may follow. It is better not to use it, unless 

 you have a laboratory to work in, or unless you are somewhat 

 of a chemist. Pure water, a little saliva and an old rag are all 

 that are commonly needed. 



When once cleaned they should be kept so. To do this it is 

 only necessary to protect them from the dust and from handling. 

 A touch of the finger will soil a thin cover, so that it will be 

 unfit for mounting. Microscopists have also devised special 

 boxes to hold cleaned covers, but unless the worker is doing 

 much mounting and wants the covers in abundance and within 

 easy reach, these are not necessary. Wooden blocks have been 

 suggested, in which longitudinal grooves have been cut, the 

 covers to be placed obliquely in the furrows, so that they may 

 be readily picked out by the forceps. Nothing more, however, 

 is needed than a dust-tight box lined loosely with one or two 

 layers of Japanese filter-paper. This paper is used extensively 

 by the dentists and can be had cheaply from the dealers in 



