J. G. Wood

“ With such powers as those with which we shall have to deal, it will rarely happen that, for example, a bottle of water in which no life is visible will be worth the carrying-home; whilst, on the other hand, a few months’ practice will render it not only possible, but easy, not only to recognise the presence, but to identify the genus, and often even the species, of the forms of life present. Moreover, these low powers, affording a general view of the object, allow the relation to each other of the details revealed by the power of the compound microscope to be much more easily grasped. ”

“ I speak from experience, having myself known the difficulties under which a young and inexperienced observer has to labour in so wide a field, without any guide to help him to set about his work in a systematic manner.
The objects that can be most easily obtained are those of a vegetable nature, as even in London there is not a square, an old wall, a greenhouse, a florist’s window, or even a greengrocer’s shop, that will not afford an exhaustless supply of microscopic employment. ”

“ Within the last half-century the use of the microscope, not only as an instrument of scientific research, a tool in the hands of the investigator of the finer organisation of the world of nature, nor even as an adjunct to the apparatus of the chemist or the manufacturer, but as a means of innocent and instructive recreation, has become so firmly rooted amongst us that it seems hardly necessary to advocate its claims to attention on any of these grounds. ”

“ It is not the man who possesses the best or most costly apparatus, but the one who best understands the use of that which he possesses, that will make the most successful microscopist. A good observer will discover, with only the aid of a pocket-magnifier, secrets of Nature which have escaped the notice of a whole army of dilettante microscopists, in spite of the advantages which, as regards instruments, the latter may enjoy. ”

“ CHAPTER V Starch, its Growth and Properties—Surface Cells of Petals—Pollen and its Functions—Seeds.
The white substance so dear to the laundries under the name of starch is found in a vast variety of plants, being distributed more widely than most of the products which are found in the interior of vegetable cells.
The starch grains are of very variable size even in the same plant, and their form is as variable as their size, though there is a general resemblance in those of the same plant which allows of their being fairly easily identified after a moderate amount of practice. ”

“ In the interior of the cell may generally be found a little dark spot, termed the “núcleus,” and which may be seen in Fig. 1, to which we have already referred. The object of the nucleus is rather a bone of contention among the learned, but the best authorities on this subject consider it to be the vital centre of the cells, to and from which tends the circulation of the protoplasm, and which is intimately connected with the growth and reproduction of the cell. ”

“ Let us first warn the intending observer against the use of powers higher than are required to bring out the details of the object. Mere magnification is of very little use: it increases the difficulties both of illumination and of manipulation, and, as already said, interferes with that grasp of the object which it is most desirable to obtain. Rather let the beginner lay himself out to get the very most he can out of his lowest powers, and he will find that, by so doing, he will be able far better to avail himself of the higher ones when their use is indispensable. ”

“ There can be little doubt but that if any worker, with moderate instrumental means, but with an observant mind, were to set determinately to work at the study of the commonest weed or the most familiar insect, he, or she, would by patient labour accomplish work which would not only be of value to science, but would redound to the credit of the worker. ”

“ It is a most wonderful sight, of which the observer is never tired, and which seems almost more interesting every time that it is beheld.
The corpuscles go pushing and jostling one another in the oddest fashion, just like a British crowd entering an exhibition, each one seeming to be elbowing its way to the best place. ”

“ The student of the fascinating field of pond-life will find new organisms awaiting description by the hundred, and of the old ones, life-histories to make out; if he be attracted rather to the vegetable inhabitants of the same realm, the diatoms will furnish him with the opportunity of studying, and perhaps solving, the enigma of their spontaneous movement, and of watching their development. The smaller fungi, and indeed the larger ones too, will amply repay the closest and most laborious study of their habits of life and processes of development. ”

“ Before leaving the subject I must ask the reader to refer again for a moment to the frog’s foot on Plate X., and to notice the arrangement of the dark pigment spots. It is well known that when frogs live in a clear sandy pond, well exposed to the rays of the sun, their skins are bright yellow, and that when their residence is in a shady locality, especially if sheltered by heavy overhanging banks, they are of a deep blackish-brown colour. Moreover, under the influence of fear they will often change colour instantaneously. The cause of this curious fact is explained by the microscope. ”

“ In the compound microscope the initial image, formed by the object-glass, is further magnified by another set of lenses, forming the eye-piece, by which the diverging rays of the virtual image are brought together to a focus at the eye-point; and when viewed directly, the eye sees an imaginary image, as in a simple microscope, whilst, when the rays are allowed to fall upon a screen, they form a real image of the object, larger or smaller, as the screen is farther from or nearer to the eye-point. ”

“ The old story of the goose-bearing tree is an example of how truth may be stranger than fiction. For if the fable had said that the mother goose laid eggs which grew into trees, budded and flowered, and then produced new geese, it would not have been one whit a stranger tale than the truth. Plate IX. Fig. 33, shows the young state of one of the common star-fishes (Comátula) , which in its early days is like a plant with a stalk, but afterwards breaks loose and becomes the wandering sea-star which we all know so well. ”

“ Opposite to the microscope, and about a foot away from it, is a lamp with the edge of the flame presented to the microscope, the concave mirror of which is so arranged as to receive the rays from the flame and direct them up the tube of the microscope. Upon the stage is placed a piece of ground-glass, and the mirror-arm is now to be moved up or down upon its support until the ground-glass receives the maximum of illumination, which it will do when the lamp-flame is at one conjugate focus of the mirror and the ground-glass at the other. ”

“ The marine forms are vastly more numerous, and more easily found, since not only pieces of weed upon which they grow are to be found upon every beach, but whole masses of leaf-like colonies, forming what is known as horn-wrack, may be plentifully found. Instead of the tentacles armed with sting-cells, like the anemone’s, possessed by the Hydrozoa, the Polyzoa have arms clothed with active cilia, by which the food is swept into the mouth, passing on into the stomach, and then through the intestine to another opening. ”

“ The little projections have a very curious effect under a high power, and require careful focusing to observe them properly; for the diameter of the grain is so large that the focus must be altered to suit each individual projection. Their office is, probably, to aid in fertilisation.
The seeds of plants are even easier of examination than the pollen, and in most cases require nothing but a pocket lens and a needle for making out their general structure. The smaller seeds, however, must be placed under the microscope, many of them exhibiting very curious forms. ”

“ The blood of animals is analogous in its office to the sap of plants, but differs greatly from it under the microscope. In sap there seem to be no microscopic characters, except that when a branch is cut, as in the vine, the flowing sap may contain certain substances formed in the wounded cells, such as chlorophyll, starch, and raphides; but the blood is known to be an exceedingly complex substance both in a microscopic and a chemical point of view. ”

“ The value of the polariser is very great, as it often enables observers to distinguish, by means of their different polarising properties, one class of objects from another.
If the expense of a polarising apparatus be too great for the means of the microscopist, he may manufacture a substitute for it by taking several thin plates of glass, arranging them in a paper tube so that the light may meet the surface of the lowest one at an angle of about 52°, and placing the bundle above the eye-piece to act as an analyser ”

“ The principle is simple enough, being merely to fill the blood-vessels with a coloured substance, so as to exhibit their form as they appear while distended with blood during the life of the animal. It sometimes happens that when an animal is killed suddenly without effusion of blood, as is often seen in the case of a mouse caught in a spring trap, the minute vessels of the lungs and other organs become so filled with coagulated blood as to form what is called a natural injection, ready for the microscope. ”

“ We now come to a class of Infusoria which is characterised by the possession of a complete covering of cilia, arranged in rows all over the body. The number of these is enormous; we can only glance at a few types, by mastering which the observer will, at all events, know whereabouts he is. The first we will take is the Coleps (Fig. 6) , a very common kind, whose body is marked by a series of geometrical lines, so that the organism looks very much like an elongated geographical globe. These markings are on the tunic, which is of a brownish colour. ”

“ Place upon the stage an object, preferably a round diatom or an echinus-spine, and focus it as sharply as possible. Now place the substage condenser in its jacket, and slide it up and down until the image of the object is bisected by the image of the flame.
The centre of the object will now be brilliantly illuminated by rays travelling in the proper direction for yielding the best results. The object is situated at the common focus of the microscope and the condenser, and, whatever means of illumination be adopted, this is the result which should always be aimed at. ”

“ The microscopic image, on the other hand, is a virtual image, which can be viewed by the eye but cannot be thus projected, for it is formed by an object placed nearer to the lens than the principal focal length of the latter, so that the rays diverge, instead of converging, as they leave the lens, and the eye looks, as it were, back along the path in which the rays appear to travel, and so sees an enlarged image situated in the air, farther away than the object, as shown in Fig. ”

“ When a little fresh blood is placed under the microscope, it is seen to consist of a colourless fluid filled with numerous little bodies, commonly called “blood-globules,” varying very greatly in size and shape, according to the animal from which they were taken. Those of the reptiles are very large, as may be seen at Fig. 4, Plate X., which represents a blood corpuscle of the Proteus. In this curious reptile the globules are so large that they may be distinguished during its life by means of a common pocket lens. ”

“ On the right hand of the figure is a drawing of the wood-cell found in the lime-tree (Fig. 22) , remarkable for the extremely delicate spiral markings with which it is adorned. In these wood-cells the secondary deposit is so plentiful that the original membranous character of the cell-walls is entirely lost, and they become elongated and nearly solid cases, having but a very small cavity in their centre. It is to this deposit that the hardness of wood is owing, and the reader will easily see the reason why the old wood is so much harder than the young and new shoots. ”

“ The commonest of these plants is the Diatóma vulgáre, seen in Fig. 21 as it appears while growing. The reproduction of this plant is effected by splitting down the centre, each half increasing to the full size of the original cell; and in almost every specimen of water taken from a pond, examples of this diatom undergoing the process of division will be distinguished. It also grows by conjugation. The diatoms are remarkable for the delicate shell or flinty matter which forms the cell skeleton, and which will retain its shape even after intense heat and the action of nitric acid. ”

“ In the living state they contain cells which are concerned in the growth of the bone, and these may be made evident by softening fresh bone with acid, cutting sections of it, and staining. When viewed by transmitted light the lacunæ and canaliculi are black; but when seen by dark-field illumination the Haversian canals become black, and the lacunæ are white.
As these canaliculi exist equally in every direction, it is impossible to make a section of bone without cutting myriads of them across; and when a high power is employed they look like little dots scattered over the surface. ”

“ When at ease in its mind, the animal protrudes its wheels, and by their action draws in particles of food, these passing down to the incessantly moving jaws, which act like a mill and crush the food before it passes on to be digested. The movement of the jaws may even be seen in the young Rotifer whilst still in the egg within the body of the parent, and as the egg reaches its full development other eggs again are visible within it, so that we may have three generations in one individual. ”

“ It looks, when at rest, like a broad brown ribbon of varying length. The diatoms lie across the ribbon, on edge, and slide upon each other exactly like the ladders of a fire-escape, so that the broad ribbon is converted into a fine long thread, which speedily closes up again into the original ribbon, and so da capo. The reason for this movement, and how it is effected, is absolutely unknown; indeed, nothing certain is known as to the way in which diatoms move, nor has ever a probable guess yet been made. ”

“ If lime be present there will be strong effervescence, and the separation of the spicules can only be effected by gently warming a portion of the sponge in caustic potash solution, pouring the resulting mass into water, and allowing the spicules to settle. The washing and settling must be repeated several times, and a portion of the deposit may then be taken up with a dipping-tube, spread upon a slide and dried, and then covered in balsam solution. The forms are endless, and the same sponge will often supply three or four, or even more. ”

“ The cuticle, epidermis, or scarf-skin, as it is indifferently termed, is formed of cells or scales, much flattened and horny in the upper layers, rounder and plumper below. The true skin, or “cutis,” is fibrous in structure, and lies immediately beneath, the two together constituting the skin, properly so called. Beneath lies a layer of tissue filled with fatty globules, and containing the glands by which the perspiration is secreted. ”

“ To see these ringed vessels properly, the simplest plan is to boil the rhubarb until it is quite soft, then to break down the pulpy mass until it is flattened, to take some of the most promising portions with the forceps, lay them on the slide and press them down with a thin glass cover. They will not be found scattered at random through the fibres, which elsewhere present only a congeries of elongated cells, but are seen grouped together in bundles, and with a little trouble may be well isolated, and the pulpy mass worked away so as to show them in their full beauty. ”

“ In many species the markings are so extremely minute that they can only be made out with the highest powers of the microscope and the most careful illumination, so that they serve as test objects whereby the performance of a microscope can be judged by a practical man. ”

“ Being unable to swim, these organisms are naturally to be most often found at the bottom of the collecting bottle, and it is always advisable to take up a portion of the débris with a dipping tube, which is then held upright on a slide with the finger upon it until the dirt settles on to the slide, when it is removed, a cover-glass put upon the dirt, and a quarter-inch power used for examination. ”