CHAPTER XXII
THE CHOICE AND USE OF APPARATUS AND ACCESSORIES
In this, our concluding chapter, we propose to give a few hints upon the choice and use of the microscope and its accessories, to enlighten our readers concerning stains and staining and to add such other information as is likely to be useful, information which is better supplied in a chapter of its own than scattered about our pages and probably overlooked.
The most important question concerns the choice of a microscope. In a book of this nature it is obviously impossible to recommend the wares of any one maker. Some firms are celebrated for the good wearing qualities of their instruments, some for the delicacy—not fragility by the way—of their fine adjustments and our readers must select their maker for themselves. One thing we strongly advise, be patriotic and select a British maker, it is not only a question of patriotism but of self interest, for in many respects the British instruments lead the world. Most of the manufacturers advertise in such papers as Nature, they all print excellent catalogues, a perusal of which may be a useful preliminary.
The instrument we select will depend on the use to which we intend to put it and on the length of our purse. Perhaps the question of cost will be more important to most people. An elaborate instrument is not a desirable acquisition, till we are somewhat advanced in our work at anyrate, and one of the models which most makers call Students’ Microscopes will do everything we desire. We should have at least two objectives, three if we can afford them, a 1 inch and a 1/6 inch will enable us to examine everything described in these pages, except some of the bacteria. If we wish to add a third objective we might select a 2 inch one, for quite low-power work and later we shall probably become the proud possessors of a 1/12 inch objective, but this would be of little use to us at first. Two eyepieces will complete our optical equipment. A condenser for the stage, properly known as a substage condenser is an addition which we shall appreciate, though quite interesting work may be done without it.
Our other apparatus is inexpensive and comprises, one or two dissecting knives, some needles mounted in handles, a pair of fine scissors, a pair of small forceps, a razor, one or two camel hair brushes, three or four watch glasses, slides and cover slips, and a pipette or two. A pipette, by the way, is merely a glass tube pointed at one end and cut off square at the other; at about its centre it is much wider than at the top or bottom. It is a most useful piece of apparatus for picking up small water animals which we wish to examine. By putting the pointed end of the pipette just over an Amœba, for example, and sucking gently at the other end, we shall draw some water and the animal into the swollen part of the tube. If we then place one finger over the end of the pipette to which we have applied suction we can transfer the contents wherever we wish without it running out, as soon as we remove our finger the pipette empties itself. The dissecting knives are useful for cutting up specimens before examination, the mounted needles for teasing them, that is to say tearing them into fine shreds. The brushes we may use instead of the pipette, for picking up small objects from water, or when dry. The watch glasses are useful for examining objects such as sponges, water fleas, etc., under water. They are just as satisfactory for most purposes as the specially constructed zoophyte troughs and, of course, very much cheaper. The razor is required for section cutting concerning which we will say a few words.
For section cutting, special razors are sold, they are heavy as a rule and not hollow ground. Many microscopists aver that good sections cannot be cut with a hollow ground razor, we beg to differ, however. On this point we would advise our readers to select whichever pattern suits them best; there is no need to buy an expensive razor, for our early efforts, at anyrate, will quickly dull the cutting edge and there is no advantage in going to much expense in this direction.
To cut really good sections is not difficult, it is a question of knack rather than skill; having once acquired the knack, practice will do the rest. The great point is to begin properly, some people never take the necessary trouble in their early days and, as a consequence, they never learn to cut good sections.
There is nothing mysterious about the operation, a section is merely a very thin slice. A good section for examination under the microscope should, of course, be so thin that it is transparent; it should be equally thin everywhere, not thick in some places and thin in others and it should be cut in the proper direction. The last statement requires a little explanation; suppose we wish to make a section straight across a stem, a transverse section it would be called, then we must see to it that our section is cut straight across, and not in such a manner that the portion from which the section is cut tapers in the slightest degree. Before we begin the actual section cutting we must always trim up our specimen with one of the dissecting knives and not attempt to make the surface level with the razor. As a start, let us take some moderately fleshy plant stem for we shall find it as easy to cut as anything. Our stem must not be woody, for till we have had a fair amount of practice we shall damage our razor on its hard structures; it must not be too soft or it will be crushed out of all recognition in our fingers; it should not be hollow, for solid stems are always easier to cut. Having selected our stem and the spot upon it at which we require a section, we cut straight across it at that spot with our dissecting knife, in such a manner that the cut edge is as nearly as possible at right angles to the sides of the stem. A piece two or three inches long is the most comfortable to hold.
Holding our razor firmly in the right hand we take our specimen in the thumb and index finger of the left hand. Place the side of the stem against the first joint of the index finger and slightly bend the tip of the finger round the object. The end of the stem, from which we propose to cut our section, should be slightly above the level of the index finger. With the thumb, the stem is pressed firmly against the first joint of the index finger and the first joint of the thumb must not be bent upwards. This last point is very important, as we shall see in a moment. From our description the method of holding the stem may seem somewhat cramped; it should not be so, however, and an easy position will help towards success but let it be the correct position. We may play the violin, in a manner, without learning the correct method of bowing but we can never become expert violinists unless we hold our bow properly, in the same way we can never cut really fine sections unless we hold our specimen in the correct way. We now lay our razor along the second joint of the index finger in such a manner that the heel of the razor, or a point near the heel comes gainst the end of the stem. For the first time we realize the importance of holding our specimen correctly, for the index finger forms a convenient platform on which to steady the razor. To cut our section, we, of course, press the razor towards us and, at the same time draw it outwards from heel to toe. We must never attempt to press the razor straight through the specimen, however soft the latter may be, we must always draw the razor along, at the same time as we press it through the specimen. Never cut outwards as in sharpening a pencil and never move the razor backwards and forwards as though using a saw. The outward cut will never result in a good section, a sawing movement will give a section alternately thick and thin. Should the section be somewhat tough we may find the razor slip suddenly over its surface, an event which will impress itself upon us painfully if we have forgotten the injunction not to bend the thumb, for the certain result of the slip will be the loss of a goodly portion of skin upon one’s joint. A straight thumb will be out of the danger zone of a slipping razor.
