MICROSCOPE, USES OF THE. 



MICROSCOPE, USES OF THE. 



622 



When objects are to be examined by reflected light they may b 

 placed in little glass or card-board cells, or in pill-boxes, or they ma 

 be put up in glass cells. The preparation should be placed upon 

 dark ground, which may be effected either by cutting a piece of dar 

 blue or black glazed paper of the exact size of the cell and placing i 

 within ; or the black paper may be fixed on the posterior surface o 

 the slide ; or this surface may be covered with black paint or blac 

 varnish. 



There are various methods by which preparations may be subjectei 

 to examination, and preserved as permanent objects in a moist state 

 and the different value of the various preservative solutions which ar 

 in use entirely depends upon the nature of the substance to b 

 mounted. Distilled water forms a very good fluid for some objects 

 while for the preservation of most it is necessary to immerse them in 

 water impregnated with some antiseptic agent, which is not volatile 

 at ordinary temperatures. Many again are best preserved in spirit, o 

 in a solution of some salt. It is very difficult to lay down rules which 

 will enable the observer to choose a preservative fluid for any particu 

 lar specimen. A little experience however will soon enable him to 

 judge which solution is best adapted for the purpose. 



We take the following account of several preservative solutions 

 from Dr. Beale's valuable work on the Microscope : 



Spirit and Water. Mixtures of spirit and water of various strengths 

 are required for preserving different preparations. In diluting spirit 

 distilled water only should be employed ; for if common water be 

 treated with spirit, a precipitation of some of the salts dissolved in 

 it not unfrequently takes place, rendering the mixture turbid anc 

 unfit for use. Proof spirit will be strong enough for all general pur 

 poses, except for hardening portions of the brain or nervous system, 

 when stronger spirit must be used. Two parts of rectified spirit, 

 about specific gravity '837, mixed with one part of pure water, makes 

 a mixture of sp. gr. '915--920, which contains about 49 per cent, of real 

 alcohol, and will therefore be about the strength of proof spirit. One 

 part of alcohol, 60 over-proof, to five parts of water, forms a mixture 

 of a sufficient strength for the preservation of many substances. 



Glycerine. A solution of glycerine adapted for preserving many 

 structures is prepared by mixing equal parts of glycerine with cam- 

 phor water. The latter prevents the tendency to mildew. It may be 

 used as other preservative solutions. 



Glycerine is obtained by boiling oil with litharge. The oleate of 

 lead remains as an insoluble plaster, while the glycerine is dissolved. 

 It may be rendered free from lead by passing a current of sulphuretted 

 hydrogen through it ; and the clear solution, after filtration, may then 

 be evaporated to the consistence of a syrup. 



Thwaites's Fluid. This fluid has been much employed by Mr. 

 Thwaites for preserving specimens of Damidiea; but it is also appli- 

 cable to the preservation of animal substances. 



Water 16 ounces. 



Spirits of Wine 1 ounce. 



Creasote, sufficient to saturate the spirit. 

 Chalk, as much as may be necessary. 

 Mix the creasote and spirit, stir in the chalk with the aid of a pestle 

 and mortar, and let the water be added gradually. Next add an equal 

 quantity of water saturated with camphor. Allow the mixture to 

 stand for a few days, and filter. In attempting to preserve large pre- 

 parations in this fluid, I found it always became turbid, and therefore 

 tried several modifications of it. The solution next to be described 

 was found to answer very satisfactorily. Water may also be impreg- 

 nated with creasote by distillation. It should be remarked that 

 M. Straus-Diirekheim has succeeded in preserving preparations in 

 camphor-water only. 



Solution of Naphtha and Creasote. 



Creasote 3 drachms. 



Wood Naphtha 6 ounces. 



Distilled Water 64 ounces. 



Chalk, as much as may be necessary. 



Mix first the naphtha and creasote, then add as much prepared chalk 

 ns may be sufficient to form a smooth thick paste ; afterwards add, 

 very gradually, a small quantity of the water, which must be well 

 mixed in a mortar. Add two or three small lumps of camphor, and 

 allow the mixture to stand in a lightly-covered vessel for a fortnight 

 or three weeks, with occasional stirring. Pour off the almost-clear 

 supernatant fluid, and filter it if necessary. Preserve it in well-corked 

 or stoppered bottles. 



I have some large preparations which have been preserved in upwards 

 of a pint of this fluid, for more than five years, and the fluid is now 

 perfectly clear and colourless. Some dissections of the nervous 

 systems of insects have kept excellently the nerves keeping their 

 colour well, and not becoming at all brittle. Two or three morbid 

 specimens are al.-io in an excellent state of preservation ; the colour 

 being to a great extent preserved, and the soft character of the texture 

 remaining. I have one preparation mounted in a large gutta percha 

 cell, containing nearly a gallon of this fluid. 



Solution of Chromic Acid. A solution of chromic acid will be found 

 well adapted for preserving many microscopical specimens. It is par- 

 ticularly useful for hardening portions of the nervous system previous 

 to cutting thin sections. The solution ii prepared by dissolving suf- 



ficient of the crystallised acid in distilled water, to render the liquid 

 of a pale straw colour. 



The crystallised acid may be prepared by decomposing 100 measures 

 of a saturated solution of bichromate of potassa, by the addition of 

 120 to 150 measures of pure concentrated sulphuric acid. As the 

 mixture becomes cool, crystals of chromic acid are deposited, which 

 should be dried and well pressed on a porous tile, by which means the 

 greater part of the sulphuric acid is removed, and the crystals obtained 

 nearly pure. 



Preservative Gelatine. 



Gelatine ....... 1 ounce. 



Honey . 4 ounces. 



Spirits of Wine ounce. 



Creasote 6 drops. 



Soak the gelatine in water until soft, and to it add the honey, which 

 has been previously raised to the boiling-point in another vessel. Next 

 let the mixture be boiled, and after it has cooled somewhat the crea- 

 sote dissolved in the spirits of wine is to be added. Lastly, filter 

 through thick flannel to clarify it. When required for use, the bottle 

 containing the mixture must be slightly warmed, and a drop placed 

 on the preparation upon the glass slide, which should also be warmed 

 slightly. Next, the glass cover, after having been breathed upon, is to 

 be laid on with the usual precautions, and the edges covered with a 

 coating of the Brunswick black varnish. Care must be taken that the 

 surface of the drop does not become dry before the application of 

 the glass cover ; and the inclusion of air-bubbles must be carefully 

 avoided. 



Goadby's Solution. 



Bay Salt ...... 4 ounces. 



Alum 2 ounces. 



Corrosive Sublimate .... 4 grains. 



Boiling Water 4 pints. 



Mix and filter. This solution may for most purposes be diluted 

 with an equal bulk of water. For preserving delicate preparations it 

 should be even still more dilute. 



Burnett's Solution. This fluid has been patented. Its preservative 

 properties appear to depend upon the chloride of zinc. A strong 

 solution of chloride of zinc forms a very powerful antiseptic, and also 

 possesses the property of absorbing noxious odours, &c. 



Other saline solutions. Many other saline solutions have been 

 employed by different observers. Of these, a saturated aqueous solu- 

 tion of chloride of calcium, free from iron, has been much recom- 

 mended for preserving specimens of bone, hair, teeth, and other hard 

 structures, as well as many vegetable tissues (Schacht). A solution of 

 alum in the proportion of 1 part of alum to 16 parts of water has 

 jeeu found to answer pretty well for some substances. Gannal's 

 solution, which consists of 1 part of acetate of alumina dissolved in 

 10 parts of water; solutions of common salt (1 part to 5 parts of 

 water, with a little camphor), corrosive sublimate, persulphate of iron, 

 irsenious acid, sulphate of zinc, and solutions of several other salts, 

 lave been recommended as preservative solutions, but their employ- 

 ment has not been always attended with the most satisfactory results. 

 Arseniuretted hydrogen gas has also been recommended for the 

 reservation of animal substances, but it is not adapted for micros- 

 copical preparations. 



Canada balsam forms a most useful agent for mounting various 

 ubstances ; and the structure of many can only be clearly made o'-.t 

 when they are examined in this menstruum. 



In this method of mounting objects no cells whatever are requisite, 

 e balsam should be pale and old. The glass slides must be warmed 

 >efore the balsam is put on, and for this purpose the glasses may be 

 leld in a pair of wooden forceps, or in a pair of common forceps, the 

 egs of which are covered with cork, and heated over a spirit-lamp, or 

 ipon a brass-plate. The latter plan is the most convenient when 

 everal preparations are to be mounted at the same time, because 

 hey may be arranged in a row along the plate, and the balsam placed 

 pon each slide as it becomes hot. 



The Canada balsam may be heated after it is placed upon the slide, 

 n order to allow the air-bubbles entangled in it to rise to the surface 

 efore it is applied. 



The slide being warm, and the small quantity of Canada balsam 

 ufficient to contain the preparation having been placed upon it, it 

 lust be gently moved about while the balsam is hot and quite fluid, 

 ntil all the air-bubbles have floated to the surface and collected 

 ogether towards one spot. A pointed wire or needle should then be 

 iken, and all the bubbles either drawn out upon the end of it, which 

 lay be readily effected, or broken by the wire after it has been heated, 

 u those cases in which the preparation is not detached from the 

 ass slide upon which it has been allowed to dry, it is only necessary 

 to place the drop of balsam upon it and gently warm it, following 

 the usual precautions ; afterwards the thin glass cover may ba applied. 

 When the preparation has been dried S3parately over the water-bath 

 and cleaned, it may be taken in a fine pair of forceps, gently warmed, 

 and carefully placed in the hot and perfectly fluid balsam. After it 

 has been thoroughly wetted by the balsam, and all adhering air- 

 bubbles removed, it may be placed in the position it is intended to 

 occupy. The thin glass cover, adapted to the size of the preparation 



