PREPARATION. 



[ 531 ] 



PRESERVATION. 



useful to the microscopist, consisting of a 

 piece of thick and stout glass tube, closed at 

 one end, containing a tight-fitting piston, 

 with a valve opening upwards; the object 

 being placed in water (or other liquid) at the 

 bottom, a single raising of the piston, or at 

 all events, two pulls, will draw out all the 

 air, and the water will take its place as the 

 piston is lowered. This apparatus may be 

 used also for saturating dry objects with oil 

 of turpentine (for mounting in balsam), or 

 with oil, to produce transparency. 



Sections of woods, &c. which are to be 

 mounted in liquids, should be soaked for 

 some little time in spirit or turpentine, to 

 remove resins, &c. A special apparatus is 

 made for slicing such objects, but this is not 

 of much use except when large numbers of 

 very perfect sections of the same kind are 

 required for purposes of sale, &c. 



It need scarcely be said that sections re- 

 quire to be made in various directions in 

 studying objects by these means. Thus 

 stems should be sliced horizontally, and per- 

 pendicularly both parallel to the medullary 

 rays and at right angles to them, &c. 



The structure of laminated shells, &c. 

 may often be seen in fragments broken off 

 by the point of a knife. But sections of 

 shell, bone, &c. are best made by sawing off 

 thin pieces with a frame-saw having a watch- 

 spring blade, grinding them down upon a 

 water-of-Ayr or some other stone, and po- 

 lishing them upon a clean leather-hone or 

 strop with putty-powder and water, finally 

 upon a dry hone alone. 



Sections of very hard substances, as agate, 

 &c., are so easily made by jewellers, that a 

 description of the process is scarcely neces- 

 sary. They are made by means of a circular 

 iron plate, made to rotate by a lathe, its 

 margins being coated with a mixture of oil 

 and diamond dust. They are then ground 

 upon a plate of metal with emery-powder 

 and water, and polished upon a flat surface 

 of pitch with putty-powder and water. 



In grinding and polishing sections of hard 

 structures, it is often requisite to cement 

 them to a slide with Canada balsam, heat 

 being applied until the balsam has become 

 so hard as to fix the section firmly to the 

 slide. As soon as one side has been polished, 

 the section is removed from the slide, the 

 balsam being rendered soft by heat, the po- 

 lished side cemented to the glass, and the 

 other side polished. The balsam may after- 

 wards be separated from the section by ma- 

 ceration in oil of turpentine, aether, &c. 



PRESERVATION, of microscopic ob- 

 jects. Under this head we shall consider 

 the arrangement of microscopic objects for 

 permanent preservation, or the MOUNTING 

 of them, as it is called, supposing that they 

 have been prepared (PREPARATION) in such 

 manner as to render this desirable. We shall 

 first notice 



Dry objects, or those which exhibit their 

 structural peculiarities in the dry state. 

 These are sometimes mounted alone, at 

 others when immersed in some preservative 

 compound. 



1. In the dry and uncovered state, they 

 are occasionally mounted upon disks of cork, 

 leather, or pasteboard, the surface upon 

 which the object is to be placed being black- 

 ened by a coating of very fine lamp-black 

 mixed with warm size or gum-water, or by 

 a piece of dull black paper pasted upon it ; 

 the simplest way of making the disks is to 

 paste black paper upon thick soft leather, 

 and cut out the disks with a punch, like gun- 

 wads. The object is fastened to the disk 

 with a little solution of marine glue in naph- 

 tha or gum. The disks are sold in the shops. 

 They are usually transfixed with 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 disadvantage, 

 however, is that the objects are liable to in- 

 jury, and become covered with dust. It 

 answers very well for common objects, seeds, 

 minute lichens, &c.; but when the objects 

 are of value, they should be mounted in a 

 cell. 



2. 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, fastened 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. 



3. When the objects are minute or very 

 thin, the square 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 



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