Mr. Spencer slightly modifies the above, using wood jaws and wedge, which the following engraving will best explain. DR. MATTHEWS' TURNTABLE, TWO-THIRD SIZE. 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; and when out of use they may be protected by being thrust into a piece of cork. In laying out animal tissues that have been stained by nitrate of silver or chloride of gold, it is advisable to employ a small rod of glass drawn out to a point, as the use of a metallic point causes a deposit of gold or silver at the place of contact, which disfigures the preparation. 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 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 manipu lations, 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. Almost every scientific man, however, has his own model, and it may be as well to examine one or two of them. Mr. Goode uses the following: A, a piece of wood 8 in. long and 1⁄2 in. thick. B, a spring made with thin iron wire. The end of the spring is driven into the table, as at C. A piece of -in. iron wire is then run through the springs, which forms an axis to work upon, and also keeps them in their places. He inserts a pin at the side of the spring, so that it will fall on a given spot, and not rub the cover from side to side. The springs are made by binding the thin wire round the -in. rod about four or five times. |