242 MOUNTING OF OBJECTS. 



and sometimes to the perviousness of some part of the cement, 

 which has allowed a portion of the contained flu id to escape, and 

 air to find admission. In either case, so soon as an air-bubble 

 is seen in such a preparation, the attempt should be made to 

 prevent its increase, by laying on an additional coat of varnish ; 

 but if this should not be successful, the cover should be taken 

 off, and the specimen remounted, so soon as the fluid has 

 escaped to such a degree as to leave any considerable portion of 

 it uncovered. 



140. Importance of Cleanliness. The success of the result of 

 any of the foregoing operations is greatly detracted from, if, in 

 consequence of the adhesion of foreign substances to the glasses 

 w r hereon the objects are mounted, or to the implements used in 

 the manipulations, any extraneous particles are brought into 

 view with the object itself. Some such will occasionally present 

 themselves, even under careful management ; especially fibres 

 of silk, wool, cotton, or linen, from the handkerchiefs, &c., with 

 which the glass slides may have been wiped, and grains of starch, 

 which often remain obstinately adherent to the thin glass covers 

 kept in it. But a careless and uncleanly manipulator will allow 

 his objects to contract many other impurities than these ; and espe- 

 cially to be contaminated by particles of dust floating through 

 the air, the access of which may be readily prevented by proper 

 precautions. It is desirable to have at hand a well-closed cup- 

 board furnished with shelves, or a cabinet of well-fitted drawers, 

 or a number of bell-glasses upon a flat table, for the purpose of 

 securing our glasses, objects, &c., from this contamination, in 

 the intervals of the work of preparation ; and the more readily 

 accessible these receptacles are, the more use will the Microsco- 

 pist be likely to make of them. Great care ought, of course, to 

 be taken, that the liquids employed for mounting should be 

 freed, by effectual filtration, from all floating particles ; and both 

 these and the Canada balsam should be kept in well-closed 

 bottles. 



141. Labelling and Preserving of Objects. Whenever the 

 mounting of an object has been completed, its name ought to 

 be at once marked on it, and the slide should be put away in its 

 appropriate place. Some inscribe the name on the glass itself, 

 with a writing diamond ; whilst others prefer to gum a label ! on 

 the slide ; and others, again, cover one or both surfaces of the 

 slide with colored paper, and attach the label to it. In the case 

 of objects mounted dry or in balsam, the latter method has the 

 advantage of rendering the glass cover more secure from dis- 

 placement by a slight blow or "jar," when the varnish or balsam 

 may have become brittle by the lapse of years. Instead, how- 

 ever, of attaching the white label on which the name of the ob- 

 ject is written, outside the colored paper with which the slide is 



1 Very neat gummed labels, of various sizes and patterns suitable to the wants of the 

 Microscopist, are sold by the " Drapers' Stationers" in the City. 



