306 MANIPULATION. 



three inches or more above the flame. In some cases, the 

 iron plate described at page 271 for cementing cells will be 

 useful for melting the balsam ; but care must be taken in the 

 application of the heat, lest the balsam be made to boil after 

 the specimen is placed in it, especially if it be a portion of a 

 soft animal tissue ; if, however, it be some hard structure that 

 heat win not injure, a little boiling wiU be of no consequence. 

 A metal vessel fiUed with boiling water (as a common water- 

 plate) answers very well. 



An old knife, with a tolerably flat edge, that may be warmed 

 in the spirit lamp, will be very useful for scraping away super- 

 fluous balsam. A small bottle of turpentine, and a still smaller 

 quantity of sulphuric ether, are also necessary ; the former will 

 be in constant requisition. 



To Mount Sections of Wood. — These must be well dried 

 before they are put into balsam, especially such as have been 

 cut from green wood; very transparent sections should be 

 charred or dyed brown by one of the methods before de- 

 scribed ; we must then proceed as follows : — 



The glass slide having been wiped perfectly clean with a 

 linen rag or chamois leather, may be taken hold of at one 

 end by the wooden forceps, and slightly warmed over the 

 lamp, and a small but sufficient quantity of Canada balsam 

 placed upon it ; the glass is to be slowly warmed again, untU 

 aU trace of air bubbles in the balsam has entirely disappeared; 

 it may now be put aside for a moment or two, and when the 

 balsam is sufficiently cool, the section may be deposited in 

 it, and be adjusted to its proper place by the needle point. If 

 there be no air bubbles, the cover previously warmed on its 

 under surface may be laid upon the balsam and carefully 

 pressed flat with the end of the handle of the needle-holder, to 

 squeeze out all the superfluous balsam, care being taken to 

 preserve the section, if possible, in the middle of the slide; 

 it win be seen whether, in pressing the cover, the section 

 keeps in its place, or shifts from one side to the other, the 

 pressure must then be so contrived as to keep it in the middle ; 

 this rnay often be managed by moving the cover first to one 

 side, then to the other, until the section is brought to the 



