OF MICROSCOPIC OBJECTS. 27 



CHAPTER II. 



TO PREPARE AND MOUNT OBJECTS " DRY." 



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 dif- 

 ferent shapes and groups ; many insects lose their scales, which 

 constitute their chief value to the microscopist ; even the 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 slides which have been mounted quickly ; the objects not 

 being thoroughly dry when enclosed in the cell. Many of the 

 cheap slides are thus rendered worthless. Even with every care 

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



For the purpose of mounting opaque objects " dry," discs were 

 at one time very commonly made use of. These are circular 

 pieces of cork, leather, or other soft substance, from one-quarter 

 to half an inch in diameter, blackened with varnish or covered 

 with black paper, on which the object is fixed by gum or some 

 other adhesive substance. They are usually pierced longitudi- 

 nally by a strong pin, which serves for the forceps to lay hold of 

 when being placed under the microscope for examination. Some- 

 times objects are affixed to both sides of the disc, which is rea- 

 dily turned when under the object-glass. The advantage of this 

 method of mounting is the ease with which the disc may be 



