INFtrSOEIAl ANIMALCULES. 113 



procured a munber of these glass slides, which may have their edges 

 ground and polished. Procure some thin glass either in slips or discs 

 for covers. 



Next provide yourself with suitable cement or thick varnish to 

 connect the two. Some preparers use the painters white lead to form 

 a shallow cell, which holds the specimen with a drop of preservation 

 fluid. Others use " gold size," which they thicken with lamp black, 

 or litherage. When deeper cells are required, but which are rare for 

 Infusoria, thin slices of glass tube, or rings of gutta percha, cemented 

 to the shdes with Canada balsam, or varnish are used. In any case 

 the operator will, by the use of his judgment, and a little ex- 

 perience, soon find a method to suit his piu-pose. It is, therefore, un- 

 necessary to enter into minutise. The desirata is a substance which, 

 when indurated, is sti'ong and not brittle, and second, the filling the 

 cell so that no air be left in it. 



In all cases where Canada balsam, or any other substance that 

 indurates can be xiscd forpresenong objects, cells of fi.uid should not 

 be employed. That tliis remark is connect, may be infeiTed from the 

 very general use of Canada balsam, a substance which I Gist pro- 

 posed for that pui^jose, and gave to the public after many previous 

 ti'ials with giun and varnishes. 



For fiu'ther particulars on this subject, see " Microscopic Cabinet" 

 and "Microscopic Objects." 



Section XII. — To mount Infusoria as Ojmque Bodies. — Tliis method 

 of mounting appHes principally to the siliceous shells of the Bacillaria. 

 It consists of fixing by gum or vamish, to a black disc or cylinder, 

 the specimens to be examined. '^VTiere this plan can be adopted, it 

 is always desu-able, as it affords a more con-ect \'iew of the structui-e 

 of the siu-face, indeed it is the best verification that can be obtained. 

 In some cases fragments of the earths containing Navicidce, Campih- 

 disca, &c., may be mounted without separation ; in other cases, the 

 shells may be separated by solution of the lime and foreign matter, 

 and only the washed shells mounted. 



