ABSTRACT
We welcome the appearance of another part—the third—of Professor Reinicke’s useful contributions to microscopy, and the more warmly because the present part contains some observations of greater interest, perhaps, to English microscopists than were those embraced in the former parts. Judicious as were the previous notices, and useful, no doubt, as they would be to many, they were, for the most part, of too elementary a nature to be of much interest to the majority of English microscopists, who, furnished so abundantly by our microscope makers with every variety of contrivance and adjunct to the instrument, would not require to be told much of the very simple matters which have formed, for the most part, the subject of M. Reinicke’s former lucubrations.
In the present part, however, we observe several things which will be found as interesting and useful to many in this country, as in Germany; and of the substance of these observations we shall proceed to give a brief summary. The subjects treated of, are—
1. A cheap Polarizing Apparatus.
2. Observations on Nobert’s Test and Modern Objectives.
3. On Atmospheric Micrography.
4. On a New Method of making Preparations,
5. Miscellaneous Notices.
1. The polarizing apparatus described and recommended for general use by M. Reinicke is constructed on the principle of one constructed on a larger scale by Mr. Andwith, and with which most persons are, doubtless; familiar.
Polarization of the light in this form of apparatus is effected by its repeated reflection at an angle of 36° from the surfaces of numerous super-imposed pieces of glass, or by its transmission through similar pieces placed in the proper angle. As is well known, many pleasing experiments in polarized light may be thus performed at a very trifling cost.
Taking advantage of the same principle, M. Reinicke has contrived a polarizing apparatus, which can be adjusted to almost any microscope, made by anyone gifted with the least ingenuity, and at a very trifling cost, and which yet, according to what he says, is capable of performing nearly as well as Nichol’s prisms, and better than polariscopes made of the still more expensive tourmaline. The polarizing medium is constructed of super-imposed pieces of thin covering glass, contained in a square tube of card board ; and the following directions are given for its construction :—
1. Procure ‘from fifty to’ sixty pieces of thin covering glass, of uniforpi size, and a little more than half as, long again as the fire wipe./.A convenient size, he states, is 18 + 12mm. These axe to the. carefully selected as free from veins or specks, and they should, of course, be as fiat as it is possible to procure them. The case or tube, in which they are fixed at an angle to the axis of the tube of 35° 25’’, is conveniently made of cardboard.
On a piece of this material draw the figure shown in the accompanying woodcut, which represents the four sides of the rectangular tube. These sides, it should be remarked, are not all of the same width, a, k, i, b, and c, h, g, d, being somewhat narrower than the other two.
The distance between a b, or c d, corresponds to the breadth of the glass plates, or = 12mm., whilst the width of the other two sides is equal to the length of the glass plates when placed at the proper angle, as indicated in the line I, m. The breadth b c, that is to say, the distance between the sides b i, and c b, must, in other words, be such that when a glass plate 18mm. long, is placed between them, it should form, with the axis of the tube, the angle of 35° 25”, or very nearly so. This distance can, of course, be readily found by raising a line I m, from the point x, at an angle of 35° 25” with b i, measuring off on I m, the length of the glass plate, slip, and drawing at that point another line c h, parallel with b i. Thus is obtained the width of b c, with which d e is made to correspond.
The cardboard is now to be cut nearly through, in the direction of the lines bi, c h, and dg, so that the four portions can be readily bent upon each other. The inner side of the paper should be painted black, or pasted over with black paper, and when all is dry the four sides are brought round, and the edges a k, and e f, joined with a little gum. But before the sides are joined, a narrow slip of the same, or of thinner cardboard, should be gummed across either a, b, i, k, or c, d, g, b, a short distance from one end, as at I, n. The tube being thus constructed, one of the glass slips is dropped in it, so that one end of the slip rests upon the little ledge I n, the other, of course, abutting upon the opposite side of the tube, at the proper angle. All that now remains is to drop in the requisite number of glass slips, one upon another, and to see that they come into close and parallel contact with each other. When the last glass slip has been placed, a second slip of cardboard, similar to I n, should be glued to the wall of the tube, immediately above the upper edge of the slip. The whole set will thus be secured from displacement.
The number of glass slips to be employed, varies according to circumstances. The greater the number, the more completely is the light polarized, but at the same time, its quantity is diminished, especially when the glass is not absolutely colorless. Five plates afford scarcely any polarization, but with ten a considerable effect is obvious in the change between the light and dark fields. Fifteen plates show indications of the cross in potato-starch, which is rendered very distinct by twenty, and is perfectly sharp and well defined by twenty-five slips ; whilst at the same time the field, when two polarizers are at right angles, is almost perfectly dark. Here it is generally advisable to stop. But with perfectly colourless glass as many as thirty slips may be inserted, but beyond this no apparent advantage is gained by an increase in their number.
With respect to the mode in which polarizers, constructed as above, can be adapted for use to the microscope, M. Reinicke enters into long details, in which however it is hardly necessary to follow him, as the mode must be left to be determined pretty much by the construction of the microscope. All that appears requisite to remark is, that the square tubes above described can very easily be inserted and fixed in cylindrical ones of any size, made of thick paper, coiled up and properly secured, and that these cylinders, which are quite as serviceable as those made of brass, can be fitted for use in any way that the ordinary ones containing Nichol’s prisms are. Owing however to the necessarily greater length of the glass column, it is better to insert one of the polarizers in the microscope tube between the ocular and objective, than to place it in front of the former, by which the field would of course be too much diminished for most purposes.
2. The article on Nobert’s Test-Plate, and on ObjectGlasses of recent construction, consists chiefly of a translation of the paper by Messrs. Sullivant and Wormley, which first appeared in the ‘American Journal of Science and Art’ for January, 1861, and was given in the April number of this Journal for the same year. M. Reinicke retains the opinion expressed in the second part of his “Contributions,” that the new objectives of Hartnack, so constructed as to require the immersion of the lower lens in water, are the best he is acquainted with, or are only equalled by a combination by Hasert. These, he says, are the only glasses with which he has been able to show the cross lines in a new test-object, Frustulia Saxonica. As this is an object with which we are unacquainted, we are unable to express any opinion as to its value as a test, but from what M. Reinicke states, it would appear to be one of the most difficult of the class to which it belongs. In order to obviate some misapprehensions regarding its structure, which appear to have been entertained by many to whom he had sent specimens, he communicates a few remarks concerning it. The Frust-ulia is a diatom, in form not unlike a Navícula. Like all other diatoms, it is composed of two siliceous valves, joined together into a double plate by an interposed delicate frame. In all the specimens of this object furnished by him, the valves are more or less separated from each other according to the method proposed by Gersten-berger. The valves and frame are accordingly found in various degrees of disjunction, whence are produced, besides broken fragments, three kinds of figures. 1. (a) A simple outline as it were of the diatom, without any markings at all—this is the interposed frame. 2. A similar form with sharply defined outline, hut with a well-marked longitudinal line, and having the entire surface covered with fine transverse lines. These lines however he has hitherto been unable to count, not having any objective capable of bringing them out clearly enough; and he would be much obliged, he says, to anyone who may be more successful, and who would communicate fiis results to him. 3. The third form (c) presents a much thicker outline, and a very strongly defined longitudinal costa. This is the complete diatom, consisting.of the two valves, on which it is usually more difficult to bring out the fine lines, and it consequently should not be taken as the proper test-object.
3. Thethird article also, or that on atmospheric micrography, is merely a translation of M. Pouchet’s observations on this subject, which have already appeared in our pages.*
The fourth article consists of a new method of preparing algæ and other very delicate and soft objects, especially parts of plants, &c., by C. A. Hantzsch. The method, however, does not appear to be very new in this country, however advantageous it may doubtless prove. It depends upon the principle that, in order to prevent the shrinking of soft tissues when they are immersed in a dense, non-drying fluid, such as glycerine, or a solution of chloride of calcium, it is necessary to add those media very gradually. The way this is effected by M. Hantzsch is as follows :
The mixture he employs consists of—
The spirit being lighter and more limpid than water, compensates for the greater density of the glycerine. The preparation then being placed on the glass slide in a drop of water, another drop of the above mixture is added to it. The slide is then placed in a dry place, protected from dust, and the spirit and water are allowed to evaporate, until almost the whole of the fluid is gone. A second drop of the mixture is then added, and this allowed to evaporate as before, and so on, until a sufficient quantity of the non-drying ingredient (glycerine) is left to cover the object. The slide should then be allowed to remain a day or two before the cover is put on, in. order to be sure that no evaporable part of the fluid remains. In this way M. Hantszch states that he has succeeded in preserving a great variety of delicate objects such as filamentous Algæ (Spirogyra, Vaucheria, Œdogonium, &c.), Desmidiæ, Infusoria, Hydatina, senta Carchesium, Euglena viridis, E. sanguinea {Amœba, §c.), delicate fungi and other vegetable tissues, animalcules, &c., all retaining their natural appearance in form, colour, and structure. Although in many cases it is true that the contents of the cells are somewhat contracted, they nevertheless retain their original structure; and in every case the retention of the external form may be ensured. Objects taken in the act of fission, conjunction, &c. remain in precisely the condition they were found in, and with a little care therefore, objects may be obtained, in most cases, quite as useful as the living subjects.
‘Quart. Journ. Mie. Sc.,’ No. XXII.
