COLLECTION OF SPECIMENS 171 



jelly, be careful always to keep the finger on the 

 open end of it until the other end has reached 

 the bottom of the bottle. In this way the lower 

 strata of jelly will be tapped, so to speak; and, 

 as the heat naturally causes air-bubbles to rise 

 to the upper surface, these are to a large extent 

 excluded from the pipette. 



Our slide may now be removed from the hot- 

 water bath and be allowed to cool, and in a few 

 minutes the jelly will have so far solidified that 

 the mount can be examined under the microscope, 

 when, should any defect be discovered, the jelly 

 must be remelted and the shortcoming be rectified. 

 The final process consists in removing the super- 

 fluous jelly from around the cover-glass with a 

 penknife (sloping the blade slightly away from 

 the edge of the glass so as to leave a kind of 

 bevelled edge of jelly all round the glass to allow 

 for expansion and contraction), thoroughly cleaning 

 the slide, and sealing the cover-glass round the 

 edge with some kind of varnish ; but it is advisable 

 to let the slide stand in its rough state for two or 

 three months before thus finishing it off, as the 

 jelly is more likely in this time to thoroughly con- 

 tract and settle down. The cleaning of the slide, 

 preparatory to sealing the cell, is another of those 

 operations which, though somewhat wearisome, yet 

 go far to make or mar a mount ; for if anything 

 in the nature of grease is allowed to remain on 

 the glass, the varnish cannot adhere firmly, and 



