PEESERVATION. 



[ 632 ] 



PRESERVATION. 



a little solution of marine glvie in naplitlia, 

 or •vrith pnm. The disks are sold in the 

 shops. They are usually transfixed Avith a 

 pin, by which they may be fixed in the 

 forceps under the microscope, and may be 

 fastened to the bottom of a box lined with 

 sheet-cork when not in use. The advantage 

 of this plan is its simplicity ; its greater dis- 

 advantage, however, is that the objects are 

 liable to injury, and become covered with 

 dust. It answers very well for common 

 objects, seeds, minute lichens, etc. ; but 

 when the objects are of value, they should 

 be mounted in a cell. 



The cell may be made of a square piece 

 of card-board or pasteboard, of suitable 

 thickness, with a hole punched in the mid- 

 dle, ffistened to a slide by marine glue or 

 Canada balsam — the object being fixed to 

 the slide by a little of either of the above 

 cements, and a thin glass cover cemented to 

 the card-board. Or the whole may be fast- 

 ened together with paste — first a piece of 

 black paper upon the middle of the slide, 

 then the perforated square, next the object, 

 and lastly the cover. The square of paste- 

 board may be replaced by a glass ring, a 

 perforated square of glass, or a piece of 

 sheet gutta-percha. 



When the objects are minute or very 

 thin, the squnre of pasteboard may be dis- 

 pensed with, and they may be mounted thus : 

 they are to be laid upon a slide, and a cover 

 of thin glass placed upon them ; a piece of 

 paper larger than the cover, with a portion 

 cut from the middle larger than the object, 

 is then covered Avitli paste, and a minute or 

 two allowed to elapse, that the paper may 

 become thoroughly imbued with it, the 

 superfluous paste being removed with the 

 paste-brush ; the paper with the pasted side 

 downwards is then laid upon the cover and 

 the adjacent portions of the slide, and gently 

 pressed with a cloth, that it may be accu- 

 rately applied to the glass surfaces. The 

 whole is then allowed to dry. Tlie principal 

 point in this process is the complete removal 

 of the superfluous paste before the paper is 

 applied. If this be not effected, it will be 

 drawn by capillary attraction between the 

 cover and the slide, and reaching the object, 

 will spoil it. 



A very secure method of mounting dry 

 objects which are not altered by heat, con- 

 sists in laying a ring or square of black 

 japan upon a slide, the thiclvness of the 

 layer being adapted to that of the object, 

 and applying a pretty strong or long-con- 



tinued heat until the cement becomes per- 

 fectly hard when cold. The object is next 

 placed within the ring, a cover laid on, and 

 heat applied until the cement becomesliquid. 

 Gentle pressure then brings the cement and 

 the margius of the cover into contact ; and 

 when the cement becomes cold, the cover is 

 firmly fixed to the slide. 



Another method of fastening the cover to 

 the slide is by the use of electrical cement 

 and balsam (Cements, p. 150) mixed with 

 1 or 2 parts of tallow. 



Many dry objects can be well preserved by 

 Mountiny in Canada Balsajn. — When this 

 is to be done, care must be taken that they 

 are thoroughly dry ; otherwise they will ac- 

 quire a milky appearance, from being sur- 

 rounded by minute drops of water. Some 

 objects in drying curl up or become de- 

 formed, although their minute structure 

 may not be essentially changed ; this may 

 be prevented by confining them between 

 two slides tied together with thread, or held 

 together by india-rubber rings, sealing-wax 

 applied at the two ends, or by a folded strip 

 of brass with the ends riveted. If the ob- 

 jects be of tolerable size, they are then 

 soaked in oil of turpentine kept in an oint- 

 ment-pot covered with a lid, for some hours, 

 or even days, uiitil the air is entirely dis- 

 placed froni them by the turpentine. The 

 latter will often also remove the colouring- 

 matter from some objects, as parts of insects, 

 which may or may not be desirable ; hence 

 the duration of" the process must vary 

 accordingly. A clean slide is then warmed 

 over the flame of a spirit-lamp, or upon a 

 stove, and some clear balsam placed in the 

 middle of it, and rendered more liquid by 

 further gentle heat; the object is next care- 

 fully removed from the turpentine with fu'- 

 ceps, drained and laid upon tlie warm 

 balsam. Some more balsam is then allowed 

 to fall from the warm wire (Balsaji) 

 upon the object ; and when this is well 

 covered with it, a warmed cover is gently 

 laid upon its surface. The superfluous bal- 

 sam then escapes at the sides of the cover; 

 and this sliould be aided by gentle pressure. 

 The slide is next maintained at a gentle heat 

 upon a warm mantelpiece, or a piece of tin- 

 plate, until when allowed to cool, the bal- 

 sam is perfectly hard. As soon as this is 

 the case, the superfluous portions are cut 

 away or scraped off witli a kuife, the sur- 

 faces of the glasses cleaned from any residue 

 by a cloth wetted with turpentine or ben- 

 zole, and some sealing-wax varnish applied 



