92 A MANUAL OF BACTERIOLOGY 



microscopic preparations with Hollis' glue or any 

 other cementing agent is performed with a camel- 

 hair brush and a turn-table (Fig. 28). The slide is 

 fixed with the clips of the turn-table, the table re- 

 volved, and the brush containing the cement is held 

 in a vertical position, so as to touch the edge of the 

 cover-glass. By this means a ring of the cement is 

 deposited, which dries in a day or two. The pre- 

 paration is permanently sealed, and should now be 

 labelled and placed in the cabinet. 



The various preparations of Canada balsam and 

 Dammar varnish are prepared as follows : (a) To 

 prepare xylol balsam it is necessary to dissolve 

 Canada balsam in xylol until it has the consistency 

 of treacle ; (&) benzol balsam is 

 prepared by first drying the 

 Canada balsam until it is brittle. 

 It is then dissolved in benzol 

 until it has the same consist- 

 ency as the xylol balsam. If these mounting fluids 

 get thick on keeping, they are thinned by the addition 

 of xylol and benzol respectively; (c) chloroform- 

 turpentine balsam is prepared by dissolving 3 ozs. 

 of Canada balsam in 1 oz. of chloroform and 1 oz. 

 of turpentine. If this medium gets thick, it is 

 thinned by the addition of chloroform ; (d) Dammar 

 varnish is prepared by first dissolving 1J oz. of 

 powdered gum Dammar in 1 J oz. of turpentine, and 

 filtering. At this point \ oz. of gum mastic is dis- 

 solved in 2 ozs. of chloroform, and the solution 

 filtered. The two solutions are finally mixed to- 

 gether, and again filtered. 



