30 MICROSCOPY FOR BEGINNERS. 



is, with the edges where the glass was cut, between the 

 thumb and finger of the left hand, and with a piece of 

 soft, old muslin held smoothly over the thumb and fore- 

 finger of the right hand, gently wipe both surfaces at 

 once, rotating the square when necessary. The secret 

 of success is care, gentleness, and no wrinkles. It was 

 probably a wrinkle in the muslin that ruined my three 

 months' old pet cover. But a punishment is a good 

 thing sometimes ; the microscopist who should begin to 

 think that he was skilful enough to avoid breakage of 

 covers for more than three months, might become in- 

 sufferably conceited and a nuisance to his friends. 



But a glass square, however thin, dropped on a deli- 

 cate animal or plant will often crush it, and destroy all 

 resemblance to anything that ever lived. Some means 

 must be devised for supporting it at a very short dis- 

 tance above the slip, so that the living creatures may 

 have room to move about, and the plants may not be 

 too much flattened. This is done by making a ring of 

 cement on the slip, and thus enclosing a circular space 

 called a cell, which can be made of any depth by apply- 

 ing more cement after the first application has dried, or 

 by using the cement very thickly. 



The opticians offer several kinds of cement for sale, 

 all of which are useful for special purposes ; but the one 

 that seems most convenient, and one that can be easily 

 prepared by the beginner, is simply shellac dissolved in 

 alcohol. The solution can be made as thick as is desired 

 by allowing some of the alcohol to evaporate, or it can 



