52 PREPARATION AND MOUNTING 



CHAPTER III. 



THE term " dry" is used when the object to be mounted Is 

 not immersed in any liquid or medium, but preserved in its 

 natural state, unless it requires cleaning and drying. 



I have before stated that thorough cleanliness is necessary 

 in the mounting of all microscopic objects. I may here add 

 that almost every kind of substance used by the microscopist 

 suffers from careless handling. Many leaves with fine hairs 

 are robbed of half their beauty, or the hairs, perhaps, forced 

 into totally different shapes and groups ; many insects lose 

 their scales, which constitute their chief value to the micro- 

 scopist ; even glass itself distinctly shows the marks of the 

 fingers if left uncleaned. Every object must also be 

 thoroughly dry, otherwise dampness will arise and become 

 condensed in small drops upon the inner surface of the thin 

 glass cover. This defect is frequently met with in slide* 

 which have been mounted quickly; the objects not being 

 thoroughly dry when enclosed in the cell. Many cheap 

 slides are thus rendered worthless. Even with every care 

 it is not possible to get rid of this annoyance occasionally. 

 A good plan is to fix the covers on to the cells temporarily 

 by dropping on two sides of them a composition of equal 

 parts of wax and resin : this allows of the easy removal of 

 the cover at any time, while the object thoroughly dries 

 and is protected from dust and damage. 



For the purpose of mounting opaque objects " dry '* 

 discs were at one time very commonly used. These are 

 circular pieces of cork, leather, or other soft substance, from 

 one-quarter to half an inch in diameter, blackened with varnish 



