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The Compound Microscope: Canada

After you have practised yourself well in the handling of the microscope, your ambition will take another step, and lead you to the preparation of permanent objects. In order to set yourself up with the needful apparatus, you will have to disburse about five shillings. A small spirit-lamp will cost eighteenpence, and a small bottle of Canada balsam, another of asphalte varnish, and another of Dean's gelatine, will make about eighteenpence or two shillings more. A few pence will purchase a sheet or two of ornamental paper, and a few more a flat plate of brass or copper, about five inches by three. The rest of the five shillings may be expended in "slides" and thin glass, cut square. Slides are merely slips of glass, three inches in length by one in width, and the thin glass is used for laying upon the objects and defending them from dust. We advise the square glass, because it scarcely costs one quarter as much as the round glass, and is equally effective when properly managed. There are several methods of "putting up" preparations--namely, dry, in Canada balsam, in gelatine, and in cells. We will take them in their order. The simplest plan is, of course, the 'dry" mode. Suppose that you want to preserve a tiny piece of down, or the scales from a butterfly's wing. First wash all the slides and glasses well, by dipping them into a strong solution of soda, and then into hot water, in order to get rid rid of grease, taking care never to touch them with the hand, but to take them out of the water with the forceps. This can be done at any time, and the glasses carefully wrapped up and placed in a box ready for use.

You now select one of the slides, and lay the object exactly in its centre. If very minute objects are used, they must be examined in order to see whether they are properly disposed. The next process is, to take one of the thin glasses with the microscope, and lay it very carefully over the object. Then cut a piece of ornamental paper, about two inches long and seven-eights of an inch in width; cut or punch a circular piece out of its centre, damp it well, and cover the wrong side slightly, but completely, with paste. Lay it on the slide, so that the centre of the hole shall coincide with that of the object, work it down neatly with the fingers, and it will hold the square piece of thin glass, which is technically called the "cover," in its place. Watch it occasionally as it dries, and be ready to press down any part of the paper that may start up. Write, with ink, the name of the object on the end of the slide.

When you have made a dozen or two of these preparations, it will be time to letter and index them. On each slide paste a slip of white paper, and on the paper write a brief notice of the object, thus-- Then scratch with a bit of flint, or with a writing-diamond, if you have one, a number on the end of the slide, and have a note-book with a corresponding number, opposite to which you enter the description at a fuller length, thus:-- 18--Scales of Death's Head Moth (Acherontia Atropos), from centre of under-surface of right fore wing. Dry. June 4, 1864. + The cross signifies that you prepared the object yourself, and the reason for adding the date is, that in after years you will have a valuable guide as to the durability of your preparations. If the specimen has been purchased or presented, always add the name of the seller or donor, as well as the date. These precautions may seem to be needlessly minute, but we have so often seen whole sets of valuable preparations rendered useless for want of ticketing, that we cannot too strongly impress on our readers the necessity for the note-book as well as the label, the one acting as a check upon the other. When the label has been affixed, and the details transferred to the note-book, the ink may be washed off the end of the slide.

There is another convenient method of putting up the elytra of beetles, parts of various insects, mosses, minute shells, and similar objects. Take a common pill-box of the smallest size, and cut a little cylinder of cork, that will nearly, but not quite, equal the height of the box, and fasten one end to the bottom of the box with glue. Now blacken the interior of the box and the cork cylinder. Put a little drop of Canada balsam, Arabian cement, or gum Arabic on the top of the cylinder; put the object on it, press it into its place, and, when the cement is hard, the preparation is complete. The cover of the box serves to keep the object from dust.

Now we come to the Canada balsam, a substance which produces beautiful effects when rightly handled, but is most aggravating to the learner, causing alternate irascibility and depression of spirits. Many objects, such as the antennae and feet of insects, will not show their full beauty unless they are mounted in Canada balsam. The method of doing so is as follows:--A week or two beforehand put the objects into ether or spirits of turpentine, and allow them to remain there until wanted. Pile up some old books, or take a couple of convenient wooden blocks; lay your brass plate upon them; light the spirit-lamp, and put it under the plate so as to heat it. Lay two or three slides on the plate, and all then can be heated at the same time. Warm the bottle of Canada balsam, and with a glass rod take out a very little drop, and put it exactly in the middle of the slide. In order to insure this point, I always put a dot of ink on the wrong side of the slide. Stir it about with one of the needles mentioned on page 428, and if any bubbles rise, break them. When the balsam is quite soft and liquid, take one of the objects out of the bottle and put it into the balsam, exactly over the black dot. Now add a little more balsam, so as to cover it, and let it lie for a few moments. Take one of the glass covers, put a very little balsam on its centre, and lay it neatly over the object, pressing it down gradually and equally. Unless this be done, the object will not remain in the centre, but will shoot out on one side, and the whole operation must be begun de novo. Remove it from the hot plate and lay it on a cool surface, still continuing the pressure until the balsam has begun to harden. Lay a little leaden weight--a pistol-bullet partly flattened is excellent for the purpose--and on the cover write the name of the object, as already mentioned, and then proceed to prepare another slide. Twenty such slides may be prepared in the course of a morning, and when they are finished they should be laid carefully in a cold place, where they will be free from dust. In a week or so the balsam will be quite hard, and then the slide may be completed. Take an old knife, which should be kept for this special purpose; heat the blade in the spirit-lamp, and then run it along the edges of the slide, so as to take off the superfluous balsam which has escaped from beneath the cover. This must be done very quickly, or the balsam inside the cover will be heated by the knife, and the preparation spoiled. When this is done, cut the ornamental paper, as already described, number and label the slide, wash off the ink, and then the preparation is complete. Some objects are very troublesome to prepare, and require to be soaked in turpentine and boiled repeatedly in the balsam before they are completely penetrated with it. Objects which are put up in Deane's gelatine are managed after a similar fashion, save that the gelatine is to be heated by placing the bottle in hot water, and that the turpentine is not needed. Vegetable structures show beautifully when thus prepared. To remove the superfluous gelatine use a wet and not a hot knife.

Cells are very difficult to manage, and the novice had better not attempt to make them, but is hereby advised to purchase them ready made. Suppose that the young microscopist has dissected the digestive organs of a bee, and wishes to preserve it in spirit; his best plan will be to use a cell for the purpose. Let him buy a cell of sufficient depth, float the preparation into it, fill it up with spirit, put the cover loosely on, and leave it for a week, occasionally raising the cover and stirring the preparation with a needle, in order to get rid of any air-bubbles that may have been entangled in the tissues.

Then let him wipe the edges of the cell very dry, put on a slight layer of gold-size or asphalte varnish--the former is preferable--fill up the cell a "bumper," and lay the cover very gently upon it, beginning at one end and gently lowering it. With blotting-paper the liquid that escapes must be removed, the edges dried afresh, a flattened bullet placed on the cover, and with a very small camel's-hair brush the slightest possible coating of size painted round the edge of the cell. When it has hardened another may be given. and so on, until a thick hard wall of size has been built up round the edges and made the cover completely air-tight.

We presume that the reader does not intend to use his microscope merely as a toy, but that he desires to gain some insight into the works of Nature, and is therefore willing to set to work in a systematic manner. It is now known that both animal and vegetable structures are built up by means of certain minute particles, technically called CELLS, and that in every part of a plant or of an animal can be recognised the constituents of which it is formed. We will, therefore, begin with the vegetables. Some of the lowest plants, such as the minute algae that inhabit the water, afford excellent examples of the simple vegetable cell; but as these plants are not readily procured by a beginner, we will select some familiar object wherein the cells may be found. If any soft and pulpy fruit be taken when it is quite ripe, and submitted to the microscope, the vegetable cell will be seen in a tolerably perfect form. The three rounded objects shown in the accompanying illustration are cells from the strawberry, specimens of which can easily be seen, if a very thin slice be cut with a razor or lancet, the latter being the preferable instrument. Be careful to dip the blade in water before cutting the fruit, and to float the slice from the blade to the glass slide by placing them both under water. Unless this precaution be taken, the section will not be flat, but will be crumpled up, and the cells will not be properly seen.

Within each of these cells may be seen a small rounded object, which is technically called the "nucleus;" and in some cases a smaller nucleus, called the "nucleolus," may be observed within the nucleus itself. The increase of cells mostly takes place by a process of division. A line passes across the nucleus, which presently separates into two distinct parts, each of which recedes from the other, causing the cell to enlarge and alter its shape. Presently a line is seen across the cell itself, and in due time the cell is also divided into two parts, each having its own nucleus. In the present instance the cell is totally spherical, because the fruit from which it was taken was soft, and allowed the constituent cells to expand. When, however, the vegetable substance becomes hard, the cells are pressed closely together, and their shapes are very much altered. Sometimes, when the cells are of nearly the same size, and the pressure is equal on every side, the cells form regular twelve-sided figures, called "dodecahedra," which, when that occurs, show a six-sided outline. A very thin slice of raw potato will show the twelve-sided cells beautifully, and has the further advantage of exhibiting the starch globules with which the cells are filled. Here is a figure of a potato cell, which presents a six-sided outline, just like that of a bee's waxen dwelling, and which is crowded with the beautiful globules of starch. If the reader likes to make a few dozen balls of clay, and to squeeze them together in a mass, he will find that the central balls will have lost their globular shape, and assumed a more or less regular twelve-sided form, very much like that of the potato cells.