THE MICROSCOPE AND ITS PARTS. 3I 



ble for this method of preservation, arrange the speci- 

 men in the cell, place the cover over it — (preferably a 

 circle in this case), the diameter of the cell being a lit- 

 tle greater than that of the cover, so that the cement 

 may project a short distance beyond the edges of the 

 thin glass, and with a camel's-hair brush paint a thin 

 layer of shellac over the place where the cover and 

 ring meet. There should be but little cement on the 

 brush for the first coat, because if too much is used, or 

 if too thin, it will probably run into the cell by capil- 

 lary attraction and spoil the object. This is the one 

 great trouble in all microscopical mounting. But after 

 the first coat is dry another is to be added, and re- 

 peated until the cover is firmly fastened to the ring. 

 "Brown's Rubber Cement," for sale by the dealers, is 

 useful for this purpose, as it is very fluid, dries with 

 great rapidity, and has little tendency to "run under." 



The cell having been made, the object is to be 

 placed within it in a drop of water, the thin cover 

 dropped over it, and the preparation will then be 

 ready for examination. But how is this minute, gen- 

 erally invisible object to be got into the cell ?. A glass 

 tube about one-tenth inch in inside diameter, and as 

 long as may be convenient, several needles in wooden 

 handles, and a camel's-hair brush with a small smooth 

 stick thrust into the quill, will be needed. 



The needles are used for spreading any small mass 

 evenly over the cell, and in disentangling and arrang- 

 ing the parts of any comparatively large object, as 

 well as for lifting the thin cover from the cell so that 

 it can be easily seized by the fingers, or for tilting it 

 up in the box, where the thin squares should always be 

 kept. Fresh-water Algse (Chapter III.), for instance, 



