328 MANIPULATION. 



When It is necessary to examine the bone cells of frag- 

 ments of fossil bone, chippings only are required ; these may 

 be produced by striking the bone with the edge of a small 

 hammer, then carefully selecting the thinnest of the chips, and 

 placing them at once without any grinding in Canada balsam. 



Mounting Sections of Bone. — The next process is that of 

 mounting the sections; this may be done either in the dry 

 way, as described in page 316, in a thin cell in fluid, or in 

 Canada balsam. If the section be very thin, transparent, 

 and well polished, it ought to be mounted either in fluid or 

 dry; if not, the Canada balsam may be had recourse to. 

 The method of doing which is as follows: — After having 

 placed some thin Canada balsam on a slide of the required 

 size, it must be heated until it boils; it may then be laid 

 aside for a moment to cool, when the section, having been 

 previously made dry, is to be placed in it ; if the balsam be 

 too cold for the section to sink into it, a little more heat 

 must be applied, and as soon as the balsam is again fluid 

 enough, the section may be embedded in it ; should the heat 

 be such as to cause air bubbles to appear, it will then be 

 desirable to remove them before the thin glass cover is laid 

 on ; this may be done in two ways, either by drawing them 

 from the field in the neighbourhood of the object with the 

 pointed instrument, or by heating the balsam again, so as to 

 make it boil ; when the bubbles are all removed, the thin 

 glass cover, with its under surface warmed, may be laid 

 upon the balsam, and pressed down so as to exclude at the 

 same time all the air bubbles and all the superfluous balsam. 

 In some cases the author has found that sections of bone, which 

 have been laid in balsam and heated until the balsam has 

 boiled, exhibit their intimate structure more beautifully than 

 they did before the extra heat had been applied. When 

 a section is put into very liquid balsam, the bone cells 

 soon become filled, which makes the structure indistinct; 

 hence it is better to mount all bones in the dry way or in 

 fluid, except those which are of a very dark colour, and have 

 their bone cells and canals filled with earthy matter. All 

 sections of recent and greasy bones should be soaked in ether 



