THE MICROSCOPE AND ITS PARTS. 25 



ily do their work without their owner's conscious bid- 

 ding. 



The specimen to be studied may be permanently pre- 

 served, or "mounted," on a slip of glass, under a thin 

 cover and surrounded by Canada balsam, glycerine, or 

 some other preservative, thus forming preparations 

 called " slides/' or " mounted slides," the plain piece of 

 glass without the object being a "slip." The addition 

 of the object therefore changes the slip into a slide. It 

 is well to remember this distinction in talking with the 

 dealers or sending orders by mail. 



Slides can be made by the student, although to do the 

 work neatly and well demands some skill and considera- 

 ble preliminary study of the object before it can be pre- 

 pared for the mounting processes ; or the slides may be 

 purchased. It is much better arid, in the end, more sat- 

 isfactory to the owner of the slides to prepare them 

 himself. Certain rare objects, if desired, must be bought 

 already mounted, but any small object naturally dry 

 can be so easily mounted by placing it in a drop of Can- 

 ada balsam from the druggist's, and covered by a cover 

 of thin glass from the optician's, that for the beginner 

 to spend his money for " the foot of a fly," " dust from 

 a butterfly's wing," " the sting of a bee," or similar 

 slides crowding the dealers' lists and drawers, is non- 

 sense, unless he lives alone in the wilderness, and is ig- 

 , norant of the appearance of a slide ; in such a case, to 

 buy the mounted foot of a fly may be useful to show 

 what is to be aimed at in the preparation of ordinary 



