It is very probable that a beginner would ask his friend what kind of slides he would advise him to use. Almost all those made of wood are liable to warp more or less, even when the two pieces are separate or of different kinds; those of cardboard and wood are generally free from this fault, yet the slides, being opaque, prevent the employment of the Lieberkuhn. To some extent glass slides, when covered with ornamental papers, are liable to the same objection, as the light is partly hindered. And sometimes the dampness from the paste, or other substance used to affix the papers, penetrates to the object, and so spoils it, though this may be rendered less frequent by first attaching the thin glass to the slide by some harder cement. Much time, however, is taken up by the labour of covering the slides, which is a matter of consideration with some. Certainly, the cost of the glass slides was formerly great; but now they are reasonable enough in this respect, so that this objection is removed. It is, therefore, well to use glass slides, except where the thin glasses are employed for tests, &c., as above. When the thin glass circles are placed upon the slides, and the edge is varnished with black or coloured rings, the appearance of finish is perfect. The trouble is much less than with most of the other methods, and the illumination of the object very slightly interfered with.
To varnish the edges of these covers, make circles of any liquid upon the glass slide, and perform any other “circular” work mentioned hereafter, the little instrument known as “Shadbolt’s turntable” is almost indispensable. It is made as follows:—At one end of a small piece of hard wood is fixed an iron pivot about one-eighth inch thick, projecting half an inch from the wood, which serves as a centre upon which a round brass table three inches in diameter revolves. On the surface of this are two springs, about one and a half inches apart, under which the slide is forced and so kept in position, whilst the central part is left open to be worked upon. The centre is marked, and two circles half an inch and one inch in diameter are usually deeply engraved upon the table to serve as guides in placing the slide, that the ring may be drawn in the right position. When the slide is placed upon the “table” underneath the springs, a camel-hair pencil is filled with the varnish, or other medium used, and applied to the surface of the glass; the table is then made to revolve, and a circle is consequently produced, the diameter of which it is easy to regulate.
Many objects for the microscope may be seriously injured by allowing the fingers to touch them—many more are so minute that they cannot be removed in this way at all, and often it is necessary to take from a mass of small grains, as in sand, some particular particle. To accomplish this, there are two or three contrivances recommended: one by means of split bristles, many of which will readily be found in any shaving brush when it has been well used. The bristles when pressed upon any hard surface open, and when the pressure is removed close again with a spring; but the use of these is limited. Camel-hair pencils are of great service for this and many other purposes to the microscopist. In very fine work they are sometimes required so small that all the hairs with the exception of one or two finer pointed ones are removed. A few of various sizes should always be kept on hand.
Equally necessary are fine pointed needles. They are very readily put up for use by thrusting the “eye” end into a common penholder, so as to be firm. The points may be readily renewed, when injured, on a common whetstone; but when out of use they may be protected by being thrust into a piece of cork.
Knives of various kinds are required in some branches of microscopic work, but these will be described where “dissection,” &c., is treated at some length, as also various forms of scissors. In the most simple objects, however, scissors of the usual kind are necessary. Two or three sizes should always be kept at hand, sharp and in good order.
A set of glass tubes, kept in a case of some sort to prevent breakage, should form part of our “fittings” and be always cleaned immediately after use. These are generally from six to ten inches long and from one-eighth to a quarter of an inch in diameter. One of these should be straight and equal in width at both ends; one should be drawn out gradually to a fine point; another should be pointed as the last, but be slightly curved at the compressed end, in order to reach points otherwise unattainable. It is well to have these tubes of various widths at the points, as in some waters the finer would be inevitably stopped. For other purposes the fine ones are very useful, especially in the transfer of “preservative liquids” which will come under notice in another chapter.
Forceps are required in almost all microscopic manipulations, and consequently are scarcely ever omitted from the microscopic box, even the most meagrely furnished; but of these there are various modifications, which for certain purposes are more convenient than the usual form. The ordinary metal ones are employed for taking up small objects, thin glass, &c.; but when slides are to be held over a lamp, or in any position where the fingers cannot conveniently be used, a different instrument must be found. Of these there are many kinds; but Mr. Page’s wooden forceps serve the purpose very well. Two pieces of elastic wood are strongly bound together at one end, so that they may be easily opened at the other, closing again by their own elasticity. Through the first of these pieces is loosely passed a brass stud, resembling a small screw, and fastened in the second, and through the second a similar stud is taken and fixed in the first—so that on pressure of the studs the two strips of wood are opened to admit a slide or other object required to be held in position. The wood strips are generally used three or four inches long, one inch wide, and about one-eighth inch thick.
Again, some objects when placed upon the glass slide are of such an elastic nature that no cement will secure the thin glass covering until it becomes hard. This difficulty may be overcome by various methods. The following are as good and simple as any. Take two pieces of wood about two inches long, three-quarters wide, and one-quarter thick; and a small rounded piece one inch long and one-quarter in diameter; place this latter betwixt the two larger pieces. Over one end of the two combined pass an india-rubber band. This will give a continual pressure, and may be opened by bringing the two pieces together at the other end; the pressure may be readily made uniform by paring the points at the inner sides, and may be regulated by the strength of the india-rubber band. These bands may be made cheaply, and of any power, by procuring a piece of india-rubber tubing of the width required, and cutting off certain breadths. Another very simple method of getting this pressure is mentioned in the “Micrographic Dictionary.” Two pieces of whalebone of the length required are tied together firmly at each end. It is evident that any object placed betwixt them will be subject to continual pressure. The power of this may be regulated by the thickness and length of the whalebone. This simple contrivance is very useful.
Common watch-glasses should always be kept at hand. They are certainly the cheapest, and their transparency makes them very convenient reservoirs in which objects may be steeped in any liquid; as it saves much trouble to examine cursorily under the microscope, when the air-bubbles are expelled from insects, &c., &c. They are readily cleaned, and serve very well as covers, when turned upside down, to protect any objects from the dust. For this latter purpose Dr. Carpenter recommends the use of a number of bell-glasses, especially when one object must be left for a time (which often happens) in order that another may be proceeded with. Wine glasses, when the “legs” are broken, may thus be rendered very useful.
As heat is necessary in mounting many objects, a lamp will be required. Where gas is used, the small lamp known as “Bunsen’s” is the most convenient and inexpensive. It gives great heat, is free from smoke, and is readily affixed to the common gas-burner by a few feet of india-rubber tubing. The light from these lamps is small, but this is little or no drawback to their use. Where gas is not available, the common spirit-lamps may be used, which are very clean and answer every purpose.