198 THE MICROSCOPE AND ITS REVELATIONS. 



them to the glass at once, in such a manner as to make them mutually 

 support one another. l 



193. The mode in which the operation is then to be proceeded with, 

 depends upon whether the section is to be ultimately set up in Canada 

 balsam ( 210), or is to be mounted 'dry 7 ( 169), or in fluid ( 211). 

 In the former case, the following is the plan to be pursued: The flat- 

 tened surface is to be polished by rubbing it with water on a ' Water-of- 

 Ayr ' stone, or on a hone or ' Turkey '-stone, or on an ' Arkansas '-stone; 

 the first of the three is the best for all ordinary purposes, but the two lat- 

 ter, being much harder, may be employed for substances which resist it. 2 

 When this has been sufficiently accomplished, the section is to be attached 

 with hard Canada balsam to a slip of thick well-annealed glass; and as 

 the success of the final result will often depend upon the completeness of 

 its adhesion to this, the means of most effectually securing that adhesion 

 will now be described in detail. The slide having been placed on the 

 cover of the Water-bath, and the previously-hardened balsam having 

 been softened by the immersion of the jar containing it in the bath 

 itself, a sufficient quantity of this should be laid on the slide to form, 

 when spread out by liquefaction, a thick drop somewhat larger than the 

 surface of the object to be attached. The slide should then be allowed 

 to cool, in order that the hardness of the balsam should be tested. If too 

 soft, as indicated by its ready yielding to the thumb-nail, it should be 

 heated a little more, care being taken not to make it boil so as to form 

 bubbles; if too hard, which will be shown by its chipping, it should be 

 re-melted and diluted with more fluid balsam, and then set aside to cool 

 as before. When it is found to be of the right consistence, the section 

 should be laid upon its surface with the polished side downwards; the 

 slip of glass is next to be gradually warmed until the balsam is softened, 

 special care being taken to avoid the formation of bubbles; and the sec- 

 tion is then to be gently pressed down upon the liquefied balsam, the 

 pressure being at first applied rather on one side than over its whole area, 

 so as to drive the superfluous balsam in a sort of wave towards the other 

 side, and an equable pressure being finally made over the whole. If this 

 be carefully done, even a very large section may be attached to glass with- 



1 Thus, in making horizontal and vertical sections of Foraminifera, as it would 

 be impossible to slice them through, they must be laid close together in a bed of 

 hardened Canada Balsam on a slip of glass, in such positions, that when rubbed 

 down, the plane of section shall traverse them in the desired directions; and one 

 flat surface having been thus obtained for each, this must be turned downwards, 

 and the other side ground away. The following ingenious plan was suggested by 

 Dr. Wallich ("Ann. of Nat. Hist., July, 1861, p. 58), for turning a number of 

 minute objects together, and thus avoiding the tediousness and difficulty of turn- 

 ing each one separately: The specimens are cemented with Canada Balsam, in 

 the first instance, to a thin film of mica, which is then attached to a glass slide by 

 the same means; when they have been ground-down as far as may be desired, the 

 slide is gradually heated just sufficiently to allow of the detachment of the mica- 

 film and the specimens it carries; and a clean slide with a thin layer of hardened 

 balsam having been prepared, the mica-film is transferred to it with the ground 

 surface downwards. When its adhesion is complete, the grinding may be pro- 

 ceeded with; and as the mica- film will yield to the stone without the least diffi- 

 culty, the specimens, now reversed in position, may be reduced to requisite 

 thinness. 



2 As the flatness of the polished surface is a matter of the first importance, that 

 of the Stones themselves should be tested from time to time; and whenever they 

 are found to have been rubbed down on any part more than on another, they 

 should be flattened on a paving-stone with fine sand, or on the lead-plate with 

 emery. 



