PREPARATION. 



[ 631 J 



PRESERVATION. 



upon a water-of-Ayr or some other stone, i 

 and polishing: them upon a clean leather 

 hono 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 

 necessary. They are cut by means of a j 

 rotating* circular iron plate, 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 j 

 water, and polished upon a flat surface of j 

 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 bal- 

 sam, heat being applied until tiia balsam 

 has become so hard as to iix 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 polished side cemented to 

 the glass, and the other side polished. The 

 balsam may afterwards be separated from 

 the section by maceration in oil of turpen- 

 tine, benzole, &c. 



The more delicate animal tissues require 

 hardening before section. This is usually 

 produced by freezing in the section-cutter ; 

 or by maceration in chromic-acid mixture 

 (15 grs. of chromic acid to the pint of 

 water, with a pint of methylated spirit), 

 bichromate of potash (180 grs. to the pint), 

 osmic acid, or Miiller's liquid (composed of 

 220 grs. of bichromate of potash, 90 grs. of 

 sulphate of soda, and a pint of distilled j 

 water). These liquids require to be poured 

 oft' and replaced until the tissue is suffi- 

 ciently hardened. 



Great care is required in the interpreta- 

 tion of the appearances presented by minute 

 objects or portions of tissue, as to the 

 influence of the liquids in whieh they are 

 immersed ; even water often totally distorts 

 then* natural appearance, as in the case of j 

 pollen, &c. And in animal tissues, the 

 liquid of the allantois, blood-serum, or 

 iodized serum or albumen (p. 441), are 

 often useful as corresponding nearly to the 

 liquid in which they are naturally im- 

 mersed, and so producing but little change. 



Besides these methods of preparation, 

 there are those which enable the observer 

 to keep sections or minute plants and animals 

 under continuous examination without be- 

 coming dry, to provide a proper and equable 

 or even higher temperatures to parts or the 



whole of organisms, and to add gases to the 

 fluid surrounding the object. Reckling- 

 hausen's moist chamber fulfils the first 

 requirement ; and Strieker's slide, which is 

 heated by means of the galvanic current, is 

 most useful in producing constant amounts 

 of heat. Strieker's gas-chamber, slide, and 

 its conducting tubes enable carbonic acid, 

 oxygen, hydrochloric acid, or any other gas 

 to be applied to the fluid under examination. 

 A substitute for those complicated pieces of 

 apparatus, may be made by procuring a flat 

 strap-shaped piece of metal, to be fixed upon 

 the stage, with an aperture near one end corre- 

 sponding with that in the stage. The slide 

 is placed upon this, and a feeble flame of a 

 spirit-lamp applied to the other end, will 

 serve to produce the gentle heat required to 

 set in motion or continue the amoeboid 

 movements of organisms. 



The preparation of many objects requires 

 the process of dyeing or STAINING. 



BIBL. Beale, flow fyc. ; Carpenter, Mi- 

 croscope ; Frey, Mikr. ; Strieker, Hist. ; 

 Gerlach, ibid. ; Rutherford, Hist. ; Mouchet, 

 Mn. Mic. J. iii. 75; Fletnrning, Schultze's 

 Archiv, ix. 123 ; Gronland, Cornu, and 

 Rivet, Prep. Micros. (Botanical), 1871, Qu. 

 Mic. Jn. 1872, 82; L. Clarke, Phil. Tr. 

 1851 ; Minot, Mn. M. J. xviii. 97 ; Meyer, 

 Arch. Mik. An. xiii.; Moseley, Qu. Mic. Jn. 

 1872, 374, 379; Pritchard, Qu. Mic. Jn. 

 1872, 380; Ranvier, Hist, tech.-, Marsh, 

 Section-cutting ; Betz, Schultze's Archiv, ix. 

 101 ; Qu. Mic. Jn. 1873, 343 ; Gibbs, Hist. 

 1880. 



PRESERVATION of microscopic ob- 

 jects. Under this head we shall consider 

 the arrangement of microscopic objects for 

 permanent preservation, supposing that they 

 have been prepared (PBEPABATION) in 

 such manner as to render this possible. 



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. 



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 



