28 AQUATIC MICROSCOPY FOR BEGINNERS. 



attached to it as to a good friend. But a hasty move 

 while cleaning it, or a little undue pressure, finally 

 sent it on the way that thin covers often travel. 



To clean such glass without much risk of breaking, 

 take the square with two opposite edges, that 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 se- 

 cret 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 skillful enough to avoid 

 breakage of covers for more than three months, 

 might become insufferably conceited and a nuisance to 

 his friends. 



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

 cate animal or plant is likely to crush it, and to de- 

 stroy all resemblance to anything that ever lived. 

 Some means must be devised for supporting it at a 

 short distance 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 en- 

 closing a circular space called a cell, which can be 

 made of any depth by applying more cement after the 

 first application has dried, or by freely using a thick 

 cement. 



The opticians offer several preparations of the kind 

 for sale, all of which are useful for special purposes; 

 but the one that seems most convenient, the one that 



