Read Ebook: Section-Cutting A Practical Guide to the Preparation and Mounting of Sections for the Microscope Special Prominence Being given to the Subject of Animal Sections by Marsh Sylvester

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Introduction 11 On Cutting Unprepared Vegetable Tissues 12 On Cutting Unprepared Animal Tissues 13 Preparation of Vegetable Tissues 15 Preparation of Animal Tissues 16 Special Methods of Hardening 19 Cutting Hardened Tissues by Hand 19 Microtome 20 AEther Microtome 24 Section-Knife 24 Imbedding in Paraffine for Microtome 26 Employment of Microtome 29 Staining Agents 31 Carmine Staining 32 Mounting Media 36 Mounting in Glycerine 38 Uses of Freezing Microtome 42 Employment of Freezing Microtome 43 Logwood Staining 47 Absolute Alcohol 50 Clove Oil 51 Canada Balsam 51 Mounting in Balsam 53 Finishing the Slide 55

Special Methods 57 Bone 57 Brain 59 Cartilage 60 Coffee Berry 62 Fat 63 Hair 63 Horn, etc. 64 Intestine 64 Liver 65 Lung 65 Muscle 66 Orange-peel 67 Ovary 67 Porcupine Quill 67 Potato 67 Rush 68 Skin 68 Spinal Cord 69 Sponge 71 Stomach 71 Tongue 71 Vegetable Ivory 72 Wood 72 Note A, 75 Note B, 75 Note C, 76 Note D, 76 Note E, 76 Note F, 77 Note G, 77 Note H, 93 Note I, 94 Index

SECTION-CUTTING.

It is evident, therefore, that nothing can be done with such refractory materials until, by subjection to appropriate methods of preparation, they shall have been reduced to such a consistence as to render them suitable for cutting. How this is to be accomplished will depend entirely upon the physical and chemical nature of the substance to be operated upon. As the various objects differ so widely from each other in these respects, so must the methods of preparation suitable to each also vary. It is clear, therefore, that no general directions for attaining this end can be given which would be of any practical value. It is possible, however, and very convenient, to arrange the various objects into groups or classes, to the treatment of each of which certain general rules are applicable; but there will still remain a comparatively numerous series of objects whose individual peculiarities of structure will demand for them correspondingly special methods of preparation. When such objects come to be spoken of, the particular treatment most suitable to each will also be noticed.

Footnote 1:

Note A.

Footnote 2:

Note B.

Footnote 3:

Note C.

Footnote 4:

Note D.

Footnote 5:

Note E.

Footnote 6:

Note F.

Footnote 7:

See Note G.

Footnote 8:

Dr. Klein describes a kind of "lifter," made by bending some German-silver wire, but as no drawing accompanies his description, it is not easy to form a clear idea as to the form of this instrument. In the recent and philosophical work of Sch?fer, a lifter is figured, which consists of a wire stem, having attached to its end a spade-like blade. It will be observed that the spoon described in the text differs from this lifter in having one end perforated, and in this consists the real value of the implement.

Footnote 9:

Note H.

Footnote 10:

Footnote 11:

Footnote 12:

If square covers be employed, they may be fixed to the slide by a simple method much in vogue in Germany. A thin wax taper is to be lighted, and being partially inverted for a few seconds, the wax surrounding the wick will become melted. After the slide has been freed from excess of glycerine, a drop of this heated wax is allowed to fall upon each corner of the cover, and a line of the melted wax run along the margins of the cover between these points, so as perfectly to surround it. If a good coat of white zinc cement be subsequently laid over the wax a very durable, and not unornamental, line of union will have been formed.

Footnote 13:

Footnote 14:

Sections of cartilage may also be examined, without being stained, in which case the field of the microscope should be only very feebly illuminated. Or carmine staining may be resorted to--these sections show well in glycerine, or if the staining be made very deep, even Canada balsam may be employed, and with fair results.

Footnote 15:

Ralf.

Footnote 16:

"Practical Histology," 2d edit. p. 173.

Footnote 17:

Footnote 18:

See a paper by Mr. Styles in the "Pharmaceutical Journal," also "Monthly Microscopical Journal" for August, 1875.

There are two methods by which this change of angle may be made, one of which is shown in the cold chisel just figured, and the other in the razor of which a section is shown in figures 3 and 4. In the case of the cold chisel it will be seen that the tool is first formed to a thin straight wedge which is afterwards changed to one that is much more blunt. This answers very well where the ultimate angle is comparatively large or blunt, as is the case with penknives, table-knives, carving-knives, etc. But where the ultimate angle is very small this plan does not answer well, and the method shown in Fig. 3 is generally adopted. Here the ultimate angle is such that lines touching the extreme edge and the back of the blade are perfectly straight and form the actual cutting angle. In this case, therefore, the relief is obtained by hollowing out the sides of the blade, and this is done to various extents, the extremes being shown in figures 3 and 4. Fig. 3 shows a section of a razor ground on a stone 12 inches in diameter, which is as large as is generally used for this purpose. Fig. 4 is a section of a razor ground on a four-inch stone--the smallest in general use. This method of changing the angle is of course substantially the same as the first, merely differing in the mechanical device used, but it affords this important advantage that in the subsequent honing and stropping processes the back of the razor forms a perfect guide by which the ultimate angle may be determined. This is not the case with the cold chisel or the carving-knife, in both of which cases the eye and hand alone determine the cutting angle, which is therefore apt to become irregular or even rounded--the worst form of all. This will be more easily understood from the following engravings where A, Fig. 5, shows a penknife blade, as applied to an oilstone for the purpose of giving it the final edge. The angle here shown is considerably greater than that generally used, but the principle is the same. It is evident that if, in moving the blade back and forth on the stone we allow it to rock or change the angle which the blade makes with the stone's surface, the edge will become rounded as shown in Fig. 6--a form which for delicate work is useless.

If the blade be laid down flat as at B, Fig. 5, the labor of wearing away the superfluous metal will be enormous. But if the blade be hollow as Fig. 7, then the ultimate angle may be formed quickly and accurately, there being no danger of the angles being changed on account of want of skill on the part of the operator.

Footnote 19:

Holtzapffel tell us that chisels that are required for paring across the end grain of moderately soft wood are considered to hang better to the work when they have a very slight keen burr or wire edge thrown up on the face or flat side of the tool. But this does not apply to section knives.

When the knife is to be honed, the back is applied and fastened by means of two or three set screws. When laid on the hone, the edge of the knife and the lower surface of the back form the guide and regulate the cutting angle. In this way we can use a broad, thin blade and yet secure great accuracy in honing it. Such a blade has this advantage also, that it is not so liable to be rounded and thus injured by stropping as one in which the relief is obtained by hollowing out the sides.

Such, then, are the general principles which govern the construction of cutting tools, including the section knives used by microscopists. We will now give a few practical directions for selecting a knife and putting and keeping it in order.

In selecting a knife for cutting sections, regard must be had to the texture of the material that is to be cut. To attempt to cut delicate sections of soft tissues with the stout knives which are suitable for cutting sections of woody fibre would be to destroy the sections, while to reverse the operation and cut sections of wood with thin, delicate knives would result in the ruin of the knife. We have seen a most excellent knife seriously injured by an attempt to cut material that was too hard for it. The knife was very thin, and had proved most excellent in cutting sections of such material as kidney, liver, etc. An attempt was made, against our protest, to cut a section of an apple-shoot, the wood of which was mature. Before the knife had gone half way across, it bent, dug into the wood and broke, leaving an ugly gap in the middle. Experienced section-cutters know this very well, but young microscopists are not so familiar with the facts just stated, and the point is too important to be overlooked. Those, therefore, who devote themselves to microscopical studies, or who expect to make sections of materials of several kinds, differing in hardness, etc., must provide themselves with knives of different degrees of strength.

For common work, good razors are as good as anything, provided they can be obtained with straight edges. Where razors are not suitable, recourse must be had to the surgical instrument maker, though we are sorry to say that there are but few in this country that know how to forge, temper and grind a decent knife. Most of our dealers in instruments do not make the instruments they sell; they import the goods they sell with their names stamped on, and thus get a reputation as manufacturers; a special order they are unable to fill respectably. There are some exceptions, but of the majority of dealers what we have written above is true.

The points which specially demand attention in a knife for cutting sections are these: 1. Quality of the steel used; 2. Temper; 3. Form of the blade.

Of the quality of the material of which a knife is made, nothing can be determined except by actual trial. The old tests of staining with acids, examining with the microscope, etc., are worthless, or at least too crude and uncertain to be of any practical value. Color changes with the degree of polish that is produced, and, in short, there is no reliable guide. The purchaser must depend entirely upon the reputation of the manufacturer. There is plenty of good steel to be found; the trouble lies with the cutlers. They are careless and in haste, and as a consequence they burn the steel or fail to work it sufficiently, and the result is a useless tool.

The steel may be of the very best quality, however, and well forged, and yet the knife may fail from being badly tempered--too soft or too hard. If too soft, the edge is soon dulled; the knife requires to be frequently honed, and the time wasted in keeping it in order is a serious drawback. If too hard, it is impossible to give it a keen edge, for the metal crumbles away as soon as it is honed or stropped very thin, and the edge becomes ragged and dull. Good steel, well forged, may be so tempered that it will neither crumble nor become rapidly dull.

Much may be learned on this point from careful inspection of the edge, and trial on a piece of horn, such as an old razor handle. When drawn over a clean piece of horn once or twice the edge of a soft knife is completely dulled; if well-tempered it should scarcely lose its keenness. Again, when laid flat on the thumb nail and pressed, the edge ought to bend up without breaking or crumbling, and at once, when the pressure is removed, resume its original shape. The extent to which extreme hardness and durability, or toughness, may be combined, is well shown in the famous Toledo sword-blades. One of these blades will shear through an iron nail without having its edge perceptibly dulled, and yet so tough and springy is it that it may be coiled up into a hoop of several folds without breaking or receiving any permanent set. If we could only get section knives of stuff like this, it would be a pleasure to work with them.

After all, however, the only test of these two points, material and temper, is a fair trial in actual practice. Of the form of the blade, however, it is easy to judge, and there are a few points which are frequently overlooked and which give rise to errors that are attributed to other causes.

In the text we are told that "It is essentially necessary that the back and edge of the blade be strictly parallel to each other." The author undoubtedly knew what the correct form should be, but the definition he has given is not a correct mathematical statement of the conditions involved. These are as follows:

Let us consider these conditions somewhat carefully.

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