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 Sylvester Marsh

30. Fat.—Adipose tissue may be hardened in alcohol, cut in paraffine, and mounted in glycerine. If the tissue has been injected the sections may be mounted in balsam, and are then very beautiful objects, showing the capillary network encircling the fat cells.

31. Hair.—Longitudinal sections are readily made by splitting the hair with a sharp razor. It is more difficult to cut the hair transversely. This, however, may easily be done in the following manner. The hairs having previously been well soaked in æther to remove all fatty matters, a sufficient number of them must be selected to form a bundle about the thickness of a crow quill. This bundle, after being tied at each extremity with a bit of thread, is to be immersed for several hours in strong gum (§ 18,) to which a few drops of glycerine have been added. On removal, the bundle must be suspended by means of a thread attached to one end of it, in a warm place until sufficiently hard, when it is to be imbedded and cut in paraffine (§ 12). Each section, as cut, is to be floated off the knife into methylated spirit. From this it is with the aid of the spoon (§ 14) to be transferred to a slide, the spirit tilted off, a drop of absolute alcohol added, when, after a minute or two, this also is to be drained off, the section treated with clove oil, and the mounting completed as described in § 23.

32. Horn varies very much in consistence, in some instances having a cartilaginous character, whilst in others it is almost bony. In the latter case, sections will have to be ground down in the manner explained when speaking of bone (§ 26). Where the texture is less dense, recourse may be had to prolonged steeping in hot or boiling water; in some cases it will be necessary to continue the immersion for several hours. When sufficiently soft the piece of horn may, by means of bits of soft wood, be firmly wedged into the tube of the microtome, and sections cut with a razor, or what is better, with a broad and very sharp chisel. The sections are to be put between glass slips, held together by American clips (or pegs), and put away for two or three days in order to become thoroughly dry. After well soaking in good turpentine or benzole, they must be transferred to slides, the superfluous turpentine drained off, and chloroform-balsam added, etc. (§ 23). Sections of horn should, of course, be cut in different directions, but for examination with the polariscope those cut transversely yield by far the most magnificent results. Hoofs, whalebone, and allied structures should also be treated by the above method.

33. Intestine.—The method to be pursued with sections has already been described (§ 18). The ileum, however, is a very pretty object when a portion of it is so mounted as to show the villi erect. To do this it is necessary to cement to the slide, by marine glue, a glass cell of sufficient depth. This should have been prepared some time beforehand, so that the cement may be perfectly dry and hard. The cell is now to be filled with turpentine, and the piece of ileum (having been previously passed through methylated spirit and absolute alcohol into turpentine) is gently placed into it, having the villi uppermost; pour some pure and rather fluid balsam on the object at one end, and gradually incline the slide, so as to allow the turpentine to flow out at the opposite side of the cell, till it is full of balsam. Then take a clean cover, and having placed upon it a small streak of balsam from one end to the other, allow it gradually to fall upon the cell, so as to avoid the formation of air-bubbles (§ 17), and finish the slide in the usual manner.[^[15]] Or, the intestine may be dried, and mounted dry, in a cell with a blackened bottom, for examination as an opaque object.

[15]. Ralf.

34. Liver.—Small pieces of liver may be very successfully hardened by immersion in alcohol, beginning with weak spirit and ending with absolute alcohol. Cut and mount as usual.

35. Lung must be prepared in chromic acid (§ 5). For the cutting of sections the freezing microtome (§ 18) is of especial value, and should, therefore, be used. If, however, the student be not provided with this instrument, he must proceed as follows. A small piece of lung, previously deprived of all spirit, is to be immersed until thoroughly saturated in solution of gum (§ 18). A small mould of bibulous paper (§ 2), only just large enough to receive the piece of tissue, having been prepared and filled with the mucilage, the specimen is to be transferred to it. The mould, with its contents, is now to be placed in a saucer, into which a mixture of about 6 parts of methylated spirit and 1 part of water (Schäfer) is to be poured until the fluid reaches to within about a third of the top of the paper mould. In the course of several hours the surface of the mucilage will begin to whiten and solidify. As soon as this occurs more dilute spirit must be poured into the saucer, until the mould is completely submerged. In a day or two the gum will be found to have acquired a suitable consistence for cutting, when it must be removed from the spirit, the paper mould peeled off, and the mass imbedded and cut in paraffine, the sections being afterwards treated as if they had been obtained by the freezing method (§ 18). If the solidification of the gum should proceed too slowly, a few drops of pure spirit may be added to the contents of the saucer. If, on the other hand, the gum should become overhard, it will be necessary to put into the saucer a few drops of water, and repeat this until the required consistence be obtained.

36. Muscle.—Harden in chromic acid, and cut in paraffine. Transverse sections may be made to show the shape of the fibrils. Longitudinal sections will only be required in the case of injected tissues, when such sections will be found very elegant, showing, as they do, the elongated meshes of capillaries running between and around the muscular fasciculi. Mount in glycerine or balsam. To see the transverse striæ characteristic of voluntary muscle, a very good plan is to take a bit of pork (cooked or fresh), and by means of needles to teaze it out into the finest possible shreds. If these be examined in water or glycerine, the markings will be shown very perfectly.

37. Orange-peel, common object though it be, is not to be despised by the microscopist. Transverse sections must be prepared by the gum method (§ 35). These sections are not to be subjected to the action of alcohol (as this would destroy the colour), but after drying between glass slides they must be soaked in turpentine and mounted in balsam. We shall then have a good view of the large globular glands whose office it is to secrete that essential oil upon which the odor of the orange depends.

38. Ovary may be prepared in the same manner as liver (§ 34). Sections, which are to be cut in paraffine, may be stained with carmine, and mounted in glycerine or balsam. Apart from all scientific value, we know of no slide for the microscope which, even as a mere object of show, surpasses in beauty a well-prepared section of injected ovary, showing the wondrous Graafian vesicles, surrounded by their meandering capillaries.