326 MANIPULATION. 



balsam, a great amount of polish is not necessary ; it may 

 then be simply rubbed upon a strop of buff or chamois leather, 

 until the desired effect is obtained ; if, on the contrary, the 

 section is to be mounted dry, the polishing should be 

 carefully attended to, a buff leather strop, with putty powder 

 and water, must be employed, and the section rubbed upon 

 it until a perfect polish is procured. The excess of putty 

 powder about the specimen may be removed by repeated 

 washing. If the operator be provided with two hones, the 

 section may be quickly made very thin by rubbing them 

 one upon the other with the section between them; when 

 sufficiently thin, it may be pohshed in the above described 

 manner. Should, however, the section be brittle, we must 

 have recourse to a different method, to effect Its being ground 

 on the hone without fracture. For this purpose, as thin a 

 section as possible having been removed by the saw, it is first 

 to be filed and then rubbed down on the hone, and polished 

 on one side only. The section is next to be dried, and then 

 cemented to one of the narrow strips of plate-glass with 

 Canada balsam ; in order to effect this, some old balsam should 

 be procured, and a small portion laid upon the centre of one of 

 the flat surfaces of a strip of plate-glass, which is then to be 

 heated until the balsam is melted and many of the air bubbles 

 have disappeared; the glass may then be removed from the 

 flame, and when it has become slightly cool, the section, with 

 its polished surface downwards, is to be placed upon the 

 balsam, and pressed firmly down until the balsam is quite 

 cold, care being taken that the entire surface of the section be 

 in contact with the glass. A good deal of the superfluous 

 balsam may now be cut away from the sides of the section, 

 sufficient being left to hold it firmly to the glass; if it be very 

 thick, the file may be used to reduce it at first, and then it 

 may be brought down to a proper degree of thinness by the 

 hone ; as the grinding is being proceeded with, the section 

 may be from time to time examined by the microscope, and 

 when it has been found to be thin enough, this surface also 

 may be polished on the buff leather in the same way as the 

 one first described. The next step is the removal of the 



