There are many objects which would lose all their distinctive2 peculiarities3 if allowed to become dry, especially those belonging to the fresh-water Alg?, many animal tissues, and most of the very delicate animal and vegetable substances in which structure is to be shown. These must be preserved by immersion4 in some fluid; but it is evident that the fluid must be suited to the kind of matter which it is intended to preserve. As it often requires much study and trouble to obtain microscopic5 objects of this class, it is well that their preservation6 should be rendered as perfect as possible; and for this reason the CELLS, or receptacles of the fluids, should be so closed that all possibility of escape should be prevented. The accomplishment7 of this is not so easy a matter as it might appear to the inexperienced.
Before giving any directions as to the manipulation required in mounting the objects, we must consider the different liquids and cells which are requisite8 for their preservation. Of the former there are a great number, of which the principal may be mentioned.
Distilled9 Water is strongly recommended by many for Diatomace? and other Protophytes. It has been, however, stated that confervoid growths often disturb the clearness of the liquid, and on this account various additions are made to it. A lump of camphor is often left in the bottle, so that the water may dissolve as much as possible. One grain of bay-salt and one of alum are added to each ounce of water; or a drop or two of creosote shaken up with the84 ounce of water, which should be afterwards filtered. These additions are often made; perhaps each of them good for certain objects.
Glycerine.—Some affirm this to be one of the best preservative liquids, especially for vegetable objects; but others think that it is much better when diluted11 with two parts of camphor-water, prepared as above.E
E Dr. Carpenter says:—“Glycerine has a solvent12 power for carbonate of lime, and should not be employed when the object contains any calcareous structure. In ignorance of this fact, the author (Dr. C.) employed glycerine to preserve a number of remarkably13 fine specimens14 of the pentacrinoid larva of the Comatula, whose colours he was anxious to retain; and was extremely vexed16 to find, when about to mount them, that their calcareous skeletons had so entirely17 disappeared, that the specimens were completely ruined.”
Glycerine and Gum.—This is also believed to be a very good liquid for vegetable tissues, and is thus prepared:—
Pure gum-arabic 1 oz.
Glycerine 1 ”
Water (distilled) 1 ”
Arsenious acid 1? grains.
Dissolve the arsenious acid in the cold water, then the gum, add the glycerine, and mix without bubbles.
Deane’s Compound.—This is usually deemed about the best medium for preserving Alg?, mosses18, &c., and is thus prepared:—Soak 1 oz. of best gelatine in 4 oz. of water until the gelatine becomes soft, when 5 oz. of honey heated to boiling-point are added; boil the mixture, and when it has cooled, but not enough to become stiff, add ? oz. rectified19 spirit with which 5 or 6 drops of creosote have been well mixed, and filter the whole through fine flannel20. This compound when cold forms a stiff jelly, the use of which will be described elsewhere.
Glycerine Jelly.—This mixture closely resembles the above, but as the composition differs a little it may be mentioned here. It is strongly recommended by Mr. Lawrance in the Microscopic Journal, where he states “that85 the beautiful green of some mosses mounted two years ago, is still as fresh as the day they were gathered;” and that this is the only medium he knows which will preserve the natural colour of vegetable substances. He takes a quantity of Nelson’s gelatine, soaks it for two or three hours in cold water, pours off the superfluous21 water, and heats the soaked gelatine until melted. To each fluid ounce of the gelatine, whilst it is fluid but cool, he adds a fluid drachm of the white of an egg. He then boils this until the albumen coagulates and the gelatine is quite clear, when it is to be filtered through fine flannel, and to each ounce of the clarified solution add 6 drachms of a mixture composed one part of glycerine to two parts of camphor-water.
Goadby’s Fluid.—This is much used in the preservation of animal objects; and seldom, if ever, acts upon the colours. It is thus prepared—Bay salt, 4 oz.; alum, 2 oz.; corrosive22-sublimate23, 4 grains. Dissolve these in two quarts of boiling water and filter. For delicate preparations some recommend that this mixture be reduced by the addition of an equal quantity of water; but where there is bone or shell in the object the above acts injuriously upon it, in which case this fluid may be used:—Bay-salt 8 oz., corrosive sublimate 2 grains, water 1 quart.
Thwaites’ Liquid.—This is recommended for the preservation of Alg?, &c., as having little or no action on the colour, and is thus prepared:—Take one part of rectified spirit, add drops of creosote enough to saturate24 it; to this add sixteen parts of distilled water and a little prepared chalk, and filter. When filtered, mix with an equal quantity of camphor-water (as before mentioned), and strain through fine muslin before using.
Chloride of Zinc25 Solution.—In the “Micrographic Dictionary” this is stated to be “perhaps the best preservative known for animal tissues.” Persons of great experience, however, have given a very different opinion; but it is certainly very useful in many cases where a small degree of coagulating86 action is not injurious. It is used of strengths varying according to the softness of the parts to be preserved; the average being 20 grains of the fused chloride to 1 oz. of distilled water. To keep this liquid a lump of camphor may be left floating in the bottle. I have heard complaints that this mixture becomes turbid26 with keeping, but I think this must only be the case when some impurity27 has got into the bottle.
Carbolic Acid.—This substance has not been known long enough to warrant any decided28 opinion upon its merits. A solution of 1 part of acid to 20 of water has been recommended on account of its antiseptic properties.
Castor Oil.—This is a very useful preservative for crystals and other objects. Many salts are quite destroyed when Canada balsam is used with them; but very few are acted upon by this oil. To use it, it must be dropped in a sufficient quantity to cover the crystal or object to be preserved with a thin coating of oil. It may be necessary sometimes to spread it with a needle or other instrument. The thin glass should then be carefully placed upon it, so that all air may be excluded; and should any oil be forced out, owing to the quantity used being too great, it must be removed with blotting30 paper. When the edge of the thin glass cover and the surrounding parts of the slide are as clean as possible, a coating of sealing-wax varnish31 or liquid glue must be applied32 and allowed to dry. A second or even a third coating may be required, but not before the previous cover is quite dry. These varnishes33, however, are very brittle34, and it is much safer, as a finish, to use one of the tougher cements—gold-size, for instance—which will render it doubly secure.
The above are the principal liquids, &c., used for preserving objects in cells. The different cells may be here mentioned; and it is recommended that these should always be kept some time before use in order that the cement may become perfectly35 dry; and care must be taken that no cement be used on which the preservative liquid employed has any action whatever.
87Cement Cells.—Where the object is not very thick, this kind of cell is generally used. They are easily made with the turntable before described; but when the objects to be preserved are very minute, these cells need not be much deeper than the ordinary circle of cement on the slide. When, however, a comparatively great depth is required, it is sometimes necessary to make the wall of the cell as deep as possible, then allow it to dry and make another addition. Of these cements gold-size is one of the most trustworthy, and may be readily used for the shallow cells. The asphaltum and india-rubber, before noticed, I have found very durable37 when well baked, and exceedingly pleasant to work with. It may be used of such a thickness as to give space for tolerably large objects. Black japan also is much used. Many cements, however, which are recommended by some writers, are worse than useless, owing to the brittleness38 which renders their durability39 uncertain, as sealing-wax varnish, liquid-glue, &c.
The student may feel himself at a loss in choosing the cement which will give him the safest cells, many of them becoming partially40 or wholly dry in a year or two, as stated in another place. I can only give him a few general directions, and he must then use his own judgment41. Of course it would be lost labour to employ any cement upon which the preservative liquid has any action whatever. It is also a good rule to avoid those in whose composition there are any particles which do not become a thorough and intimate portion, as these unreduced fragments will almost certainly, sooner or later, prepare a road by which the liquid will escape; and, lastly, whatever cement he uses, the cells are always better when they have been kept a short time before use, as already stated.
Gutta-percha Rings have been recommended by some, as affording every facility for the manufacture of cells for liquids; but they cannot be recommended, as, after a certain length of time, they become so brittle as to afford no safeguard against ordinary accidents.
88 Often the cells must necessarily be of a large size, and for this reason are made by taking four strips of glass of the thickness and depth required, and grinding the places where these are to meet with emery, so as to form a slightly roughened but flat edge. The glass strip must also be ground on the side where it meets the plate, and each piece cemented with the marine42 glue mentioned in Chapter I. in the following manner:—On that part of the glass to which another piece is to be attached should be laid thin strips of the glue; both pieces must then be heated upon a small brass43 table, with the aid of the spirit-lamp, until the strips become melted; the small piece is then to be taken up and placed upon the spot to which it is to be attached, and so on until the cell is completed. It will be found necessary to spread the glue over the surface required with a needle or some other instrument, so that an unbroken line may be presented to the wall of the cell, and no bubbles formed. Too great a heat will “burn” the marine-glue, and render it brittle; care must be therefore taken to avoid this.
When shallow cells are required, those which are made by grinding a concavity in the middle of an ordinary slide will be found very convenient. The concavities are cut both circular and oblong; and the surface being flat, the cover is easily fastened upon it. These are now cheap, and are very safe as to leakage44.
Circular cells with a flat bottom used to be made by drilling a hole through glass of the required thickness, and fixing this upon an ordinary slide with marine-glue; but the danger of breakage and the labour were so great that this method is seldom used now, and, indeed, the rings about to be mentioned do away with all necessity of it.
Glass Rings.—Where any depth is required, no method of making a cell for liquids is so convenient as the use of glass rings, which are now easily and cheaply procurable45. They are made of almost every size and depth, and, except in very extraordinary cases, the necessity for building cells is completely done away with. These rings have both edges89 left roughened, and consequently adhere very well to the slide, this adherence46 being generally accomplished47 by the aid of marine glue, as before noticed with the glass cells. Gold-size has been occasionally used for this purpose; and the adherence, even with liquid in the cell, I have always found to be perfect. This method has the advantage of requiring no heat, but the gold-size must be perfectly dry, and the ring must have been fixed48 upon the slide some time before use. Canada balsam has also been used for the same purpose, but cannot be recommended, as when it is perfectly dry it becomes so brittle as to bear no shock to which the slide may be ordinarily exposed.
These are the cells which are mostly used in this branch of microscopic mounting. The mode of using them, and the different treatment which certain objects require when intended to be preserved in the before-mentioned liquids, may now be inquired into.
I may mention, however, that this class of objects is looked upon by many with great mistrust, owing to the danger there is of bubbles arising in the cells after the mounting has been completed, even for years. I know some excellent microscopists who exclude all objects in cells and preservative liquids from their cabinets, because they say that eventually almost all become dry and worthless; and this is no matter of surprise, for many of them do really become so. Perhaps this is owing to the slides being sold before they could possibly be thoroughly49 dry. As to the air-bubbles, I shall have something to say presently.
We will now suppose the cell employed is made by placing a glass ring upon the slide with marine glue or gold-size, and is quite dry. Around the edge of the cleaned thin glass which is to cover it, I trace with a camel-hair pencil a ring of gold-size, and also around the edge of the cell to which it is to adhere. Dr. Carpenter objects to this, as rendering50 the later applications of the gold-size liable to “run in.” All danger of this, however, is completely done away with by leaving the slide and cover for awhile until90 the cement becomes partially “fixed,” but still adhesive51 enough to perform its function (Chapter II.). With many slides this is not accomplished in less than twenty-four hours, even if left two or three days no injury whatever ensues; but with other kinds an hour is too long to leave the exposed cement, so that the operator must use his own discretion52. The liquid required may be drawn53 up by the mouth into the pointed54 tube mentioned in Chapter I., and then transferred to the cell. In the various books of instruction, the object is now to be placed in the cell; this, however, I think a great mistake, as another process is absolutely necessary before we advance so far. The cell, full of liquid, must be placed under the receiver of an air-pump, and the air withdrawn55. Almost immediately it will be perceived that the bottom and sides of the cell are covered with minute bubbles, which are formed by the air that is held in suspension by the liquid. The slide may now be removed, and the bubbles may require the aid of a needle or other point to displace them, so obstinately56 do they adhere to the surface of the glass. This process may be then repeated, and one cause, at least, of the appearance of bubbles in cells of liquid will be got rid of. The object to be mounted should also be soaked in one or two changes of the preservative liquid employed, and, during the soaking, be placed under the air-pump and exhausted57. It may then be transferred to the cell, which will probably cause the liquid to overflow58 a little. The cover with the gold size applied to the edge must then be carefully laid upon the cell, and slightly pressed down, so that all air-bubbles may be displaced. The two portions of gold-size will now be found to adhere wherever the liquid does not remain, although the whole ring may have been previously59 wet. The outer edge of the thin glass and cell must now be perfectly dried, and a coating of gold-size applied. When this is dry, the process must be repeated until the cement has body enough to protect the cell from all danger of leakage. When some preservative liquids are used, a91 scum is frequently found upon the surface when placed in the cell, which must be removed immediately before the cover is laid upon it.
I believe this method to be perfectly secure against leakage when carefully performed; and some of my friends have told me that their experience (some years) has been equally satisfactory.
In using some of the particular kinds of preservative liquids, it will be found necessary to make slight change in the manipulation. This will be best explained by mentioning a few objects, and the treatment they require.
For the preservation of the Mosses, Alg?, &c., Deane’s compound is much used, and considered one of the best media. The specimen15 to be mounted should be immersed in the compound, which must be kept fluid by the vessel60 containing it being placed in hot water. In this state the whole should be submitted to the action of the air-pump, as it is not an easy matter to get rid of the bubbles which form in and around the objects. The cell and slide must be warmed; and heat will also be necessary to render the gelatine, &c., fluid enough to flow from the stock-bottle. The cell may then be filled with the compound, and the specimen immersed in it. A thin glass cover must then be warmed, or gently breathed upon, and gradually lowered upon the cell, taking care, as with all liquids, that no bubbles are formed by the operation. The cover may be fixed by the aid of gold-size, Japan, or any of the usual varnishes, care being taken, as before, that all the compound is removed from the parts to which the varnish is intended to adhere.
The glycerine jelly of Mr. Lawrance, before mentioned, requires almost a similar treatment. “The objects to be mounted in this medium should be immersed for some time in a mixture of equal parts of glycerine and dilute10 alcohol (six of water to one of alcohol). The bottle of glycerine jelly must be placed in a cup of hot water until liquefied, when it must be used like Canada balsam, except that it requires92 less heat. A ring of asphaltum varnish round the thin glass cover completes the mounting.”
The Infusoria (see Chapter III.) are sometimes preserved in liquid; but present many difficulties to the student. Different kinds require different treatment, and consequently it is well, when practicable, to mount similar objects in two or more liquids. Some are best preserved in a strong solution of chloride of calcium61, others in Thwaites’ liquid, whilst a few keep their colour most perfectly when in glycerine alone. Many of them, however, are so very transparent62 that they present but faint objects for ordinary observance. The Desmidiace? require somewhat similar treatment, and may be mentioned here. The solution of chloride of calcium has been strongly recommended; but no preservative liquid seems to be without some action upon them. Both of the above classes of objects should be mounted in shallow cells, so as to allow as high a microscopic power as possible to be used with them.
Many of the Zoophytes which are obtained on our sea-coasts are well preserved by mounting in cells, in the manner before mentioned, with Goadby’s fluid, or distilled water with one of the additions noticed amongst the preservative liquids. For examination by polarized light, however, they are usually mounted in balsam (see Chapter III.), whilst those in cells present a more natural appearance as to position, &c., for common study.
As to the use of preservative liquids with the Diatomace? there are various opinions. Some experienced microscopists say that there is little or no satisfaction in mounting them in this way. Dr. Carpenter, however, explains this difference by his instructions as to what method should be used when certain ends are desired. He says: “If they can be obtained quite fresh, and it be desired that they should exhibit as closely as possible the appearance presented by the living plants, they should be put up in distilled water within cement-cells; but if they are not thus mounted within a short time after they have been gathered, about a sixth93 part of alcohol should be added to the water. If it be desired to exhibit the stipitate forms in their natural parasitism63 upon other aquatic64 plants, the entire mass may be mounted in Deane’s gelatine in a deeper cell; and such a preparation is a very beautiful object for the black-ground illumination. If, on the other hand, the minute structure of the siliceous envelopes is the feature to be brought into view, the fresh diatoms must be boiled in nitric or hydrochloric acid” (which process is fully29 described in Chapter II.). It is very convenient to have many of these objects mounted by two or more of the above methods; and if they are to be studied, this is indispensable. Mr. Hepworth once showed me about one hundred slides which he had mounted in various ways, for no other purpose than the study of the fly’s foot.
My friend, Mr. Rylands, successfully mounts the diatoms in the state in which he finds them, and gave me the following method as that which he always employs. He says that he has had no failures, and hitherto has found his specimens unchanged. Take a shallow ring cell of asphalt or black varnish (which must be at least three weeks old), and on the cell, whilst revolving65, add a ring of benzole and gold-size mixed in equal proportions. In a minute or two pure distilled water is put in the cell until the surface is slightly convex. The object having been already floated on to the cover (the vessel used for this purpose being an ordinary indian-ink palette), is now inverted66 and laid carefully upon the water in the cell. By these means the object may be laid down without being removed. The superfluous moisture must not be ejected by pressure, but a wetted camel-hair pencil, the size made in an ordinary quill67, being partially dried by drawing through the lips, must be used repeatedly to absorb it, which the pencil will draw by capillary68 attraction as it is very slowly turned round. When the cover comes in contact with the benzole and gold-size ring, there is no longer any fear of the object being removed, and a slight pressure with the end of the cedar69 stick of the94 pencil will render the adhesion complete, and cement the cover closely and firmly to the cell. When dry, an outer ring of asphalt makes the mounting neat and complete.
The Fungi70 have been before mentioned; but it may be here stated that some few of the minute forms are best preserved in a very shallow cell of liquid. For this purpose creosote-water may be advantageously used.
The antenn? of insects have been before noticed as being very beautiful when mounted in balsam. This is readily accomplished when they are large; but those of the most minute insects are much more difficult to deal with, and are less liable to injury when put up in fluid. Goadby’s Fluid serves this purpose very well; but, of course, the object must be thoroughly steeped in the liquid before it is mounted, for a longer or shorter time according to the thickness.
The eggs of insects afford some worthy36 objects for the microscope, amongst which may be mentioned those of the common cabbage butterflies (small and great), the meadow-brown, the puss-moth, the tortoiseshell butterfly, the bug71, the cow-dung fly, &c. These, however, shrivel up on becoming dry, and must, therefore, be preserved in some of the fluids before mentioned. To accomplish this no particular directions are required; but the soaking in the liquid about to be employed, &c., must be attended to as with other objects.
Glycerine may be advantageously used for the preservation of various insects. These should first be cleaned with alcohol to get rid of all extraneous72 matter, and then, after soaking in glycerine, be mounted with it like other objects. This liquid may also be used for the Entomostraca, which offer a wide field for study. They are to be found abundantly in ponds of stagnant73 water, &c. Some insects, such as May-flies, &c., are, however, often preserved by immersion in a solution of one part of chloride of calcium in three or four parts of water; but this has not been recommended amongst the “preservative liquids,” as the colour,95 which is often an attractive quality of this class of objects, is thereby74 destroyed.
We have now noticed the treatment which must be applied to those objects which are to be preserved in liquids and cells. We may here state that all slides of this kind should be examined at short intervals75, as they will be found now and then to require another coating of varnish round the edge of the thin glass cover to prevent all danger of leakage. The use of the air-pump, in the first instance (as before recommended), and this precaution as to the varnish, will render the slides less liable to leakage and air-bubbles, which so very frequently render them almost worthless.
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1
preservative
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| n.防腐剂；防腐料；保护料；预防药 | |
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distinctive
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| adj.特别的，有特色的，与众不同的 | |
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peculiarities
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| n. 特质, 特性, 怪癖, 古怪 | |
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immersion
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| n.沉浸；专心 | |
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microscopic
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| adj.微小的，细微的，极小的，显微的 | |
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preservation
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| n.保护，维护，保存，保留，保持 | |
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accomplishment
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| n.完成，成就，（pl.）造诣，技能 | |
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requisite
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| adj.需要的，必不可少的；n.必需品 | |
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distilled
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| adj.由蒸馏得来的v.蒸馏( distil的过去式和过去分词 )；从…提取精华 | |
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dilute
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| vt.稀释，冲淡；adj.稀释的，冲淡的 | |
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diluted
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| 无力的，冲淡的 | |
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solvent
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| n.溶剂；adj.有偿付能力的 | |
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remarkably
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| ad.不同寻常地，相当地 | |
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specimens
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| n.样品( specimen的名词复数 )；范例；（化验的）抽样；某种类型的人 | |
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specimen
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| n.样本，标本 | |
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vexed
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| adj.争论不休的；（指问题等）棘手的；争论不休的问题；烦恼的v.使烦恼( vex的过去式和过去分词 )；使苦恼；使生气；详细讨论 | |
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entirely
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| ad.全部地，完整地；完全地，彻底地 | |
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mosses
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| n. 藓类, 苔藓植物 名词moss的复数形式 | |
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rectified
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| [医]矫正的，调整的 | |
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flannel
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| n.法兰绒；法兰绒衣服 | |
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superfluous
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| adj.过多的，过剩的，多余的 | |
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corrosive
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| adj.腐蚀性的；有害的；恶毒的 | |
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sublimate
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| v.(使)升华，净化 | |
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saturate
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| vt.使湿透，浸透；使充满，使饱和 | |
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zinc
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| n.锌；vt.在...上镀锌 | |
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turbid
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| adj.混浊的，泥水的，浓的 | |
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impurity
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| n.不洁，不纯，杂质 | |
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decided
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| adj.决定了的，坚决的；明显的，明确的 | |
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fully
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| adv.完全地，全部地，彻底地；充分地 | |
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blotting
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| 吸墨水纸 | |
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varnish
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| n.清漆；v.上清漆；粉饰 | |
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applied
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| adj.应用的；v.应用，适用 | |
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varnishes
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| 清漆的面（尤指木器或金属制品上的）( varnish的名词复数 )； 光泽面； 罩光漆 | |
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brittle
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| adj.易碎的；脆弱的；冷淡的；(声音)尖利的 | |
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perfectly
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| adv.完美地，无可非议地，彻底地 | |
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worthy
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| adj.(of)值得的，配得上的；有价值的 | |
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durable
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| adj.持久的，耐久的 | |
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brittleness
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| n.脆性，脆度，脆弱性 | |
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durability
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| n.经久性，耐用性 | |
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partially
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| adv.部分地，从某些方面讲 | |
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judgment
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| n.审判；判断力，识别力，看法，意见 | |
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marine
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| adj.海的；海生的；航海的；海事的；n.水兵 | |
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brass
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| n.黄铜；黄铜器，铜管乐器 | |
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leakage
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| n.漏，泄漏；泄漏物；漏出量 | |
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procurable
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| adj.可得到的，得手的 | |
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adherence
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| n.信奉，依附，坚持，固着 | |
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accomplished
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| adj.有才艺的；有造诣的；达到了的 | |
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fixed
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| adj.固定的，不变的，准备好的；(计算机)固定的 | |
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thoroughly
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| adv.完全地，彻底地，十足地 | |
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rendering
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| n.表现，描写 | |
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adhesive
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| n.粘合剂；adj.可粘着的，粘性的 | |
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discretion
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| n.谨慎；随意处理 | |
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drawn
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| v.拖，拉，拔出；adj.憔悴的，紧张的 | |
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pointed
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| adj.尖的，直截了当的 | |
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withdrawn
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| vt.收回；使退出；vi.撤退，退出 | |
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obstinately
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| ad.固执地，顽固地 | |
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exhausted
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| adj.极其疲惫的，精疲力尽的 | |
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overflow
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| v.(使)外溢，(使)溢出；溢出，流出，漫出 | |
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previously
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| adv.以前，先前（地） | |
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vessel
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| n.船舶；容器，器皿；管，导管，血管 | |
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calcium
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| n.钙(化学符号Ca) | |
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transparent
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| adj.明显的，无疑的；透明的 | |
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parasitism
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| n.寄生状态，寄生病；寄生性 | |
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aquatic
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| adj.水生的，水栖的 | |
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revolving
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| adj.旋转的，轮转式的；循环的v.（使）旋转( revolve的现在分词 )；细想 | |
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inverted
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| adj.反向的，倒转的v.使倒置，使反转( invert的过去式和过去分词 ) | |
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quill
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| n.羽毛管；v.给（织物或衣服）作皱褶 | |
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capillary
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| n.毛细血管；adj.毛细管道；毛状的 | |
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cedar
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| n.雪松，香柏(木) | |
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fungi
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| n.真菌，霉菌 | |
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bug
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| n.虫子；故障；窃听器；vt.纠缠；装窃听器 | |
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extraneous
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| adj.体外的；外来的；外部的 | |
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stagnant
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| adj.不流动的，停滞的，不景气的 | |
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thereby
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| adv.因此，从而 | |
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intervals
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| n.[军事]间隔( interval的名词复数 )；间隔时间；[数学]区间；（戏剧、电影或音乐会的）幕间休息 | |
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