1 1 1 can be cut varying from 30, 150, 100, 75, 80, tomm. Instead of the knife supplied with the apparatus, a razor may be used. FIG. 39.-Silk Band for Catching the Chain Microtome. The sections can be received on a silk ribbon, as shown in fig. 39. This is clamped to the apparatus. The sections are received on the ribbon, which is rotated by means of a milled head. Jung's or Thoma's Microtome. -In this instrument the tissue to be cut is fixed in a clamp, the knife is fixed in another heavy clamp which moves on planed surfaces. After each section the tissue is pushed up an inclined plane by means of the milled head on the extreme right of the figure (fig. 40). Malassez's Modification of Roy's Microtome (fig. 41).-Sometimes it is desired to cut sections of Serial Sections made by Minot's of a tissue while it is under fluid, e.g., alcohol. This can be done as shown in fig. 41. The microtome is made to move on its base, and can be placed FIG. 40.--Thoma's Sledge Microtome, as made by Jung. vertically in such a way that the razor and the piece of tissue to be cut come to lie in a vessel filled with alcohol. Williams' Freezing Microtome (fig. 42). This consists of a wooden, non-conducting tub for holding the freezing mixture. Vertically in the centre of this rises a brass cylinder, into whose upper end the roughened brass plate on which the tissue is frozen can be screwed. The lid of the box is formed by a glass plate fitted into a framework or kind of cap for the tub. In the centre of the glass plate is a circular hole into which the freezing-plate projects. In this instrument the tissue remains fixed, while the knife or blade is depressed by the movement of a screw. The knife or razor is fixed in a brass tripod frame-work or knife-carrier. In using the instrument, fill the tube with the freezing mixture of ice and salt, and when the central brass pillar becomes sufficiently cooled, pour on it a little mucilage, and when this is frozen place on it the tissue, which must not be more than 1 cm. in thickness, and pencil some mucilage on it. When it is solid, the knife in the tripod is used to cut the sections; and as the front leg of the tripod consists of a screw, this is turned, and thus the cutting edge is brought to touch the tissue. Swift's Freezing Microtome (fig. 43).-A modification of the previous instrument is shown in fig. 43, which is adapted for freezing with ether. Hand-Microtome (fig. 44).-When only a few sections are required, this instrument, invented by Ranvier, is extremely convenient. The FIG. 44.-Ranvier's Hand-Microtome. tissue is embedded in the well of the instrument in paraffin or elder pith, and sections made by means of a razor, as shown in the figure. The tissue is gradually raised by means of the milled head. Section-Flatteners. Sometimes the sections saturated with paraffin when cut exhibit a great tendency to curl up. This can partly be avoided by pressing the section as it is cut gently against the knife, by means of a camel's-hair brush. Several sectionflatteners attached to the cutting-knife have been used for this purpose. Take a wire 1 mm. in diameter, heat it in a flame, and bend it twice at right angles, the distance between the angles being about an inch. The free ends are then bent round in the form of a hook. These hooks serve to fix the frame on the back of the razor, forming, as it were, a spring-clip. The part of the wire between the right angles is so arranged that it lies parallel to, and about one-hundredth of an inch from, the edge of the knife. In cutting, the section has to pass between the spring and the knife, and is thus largely prevented from curling up. Curled-up paraffin sections may be made to uncurl by being placed in water at about 40° C. (Gaskell). Cutting a Continuous Series of Sections in Celloidin.-The tissue, embedded in celloidin, is clamped in a microtome, e.g., that of Jung, and section after section is made. The knife must pass at an acute angle through the celloidin, and must be moistened with 80 per cent. alcohol. This is easily effected from a wash-bottle. Schanze of Leipzig supplies such a bottle provided with a valve, which facilitates the outflow of a gentle stream of alcohol upon the cutting blade. Weigert's method of arranging and fixing the sections on a slide is the best. Each section in celloidin as it is made is laid upon a narrow strip of curl-paper by means of a camel's-hair pencil. The curl-paper is kept moist by being placed on a plate covered with blotting-paper well moistened with 80 per cent. alcohol. The sections are laid upon the curl-paper in the order desired. A slide is coated with a layer of thin collodion, and when it is dry, the celloidin sections on the curl-paper are transferred to it. This is done by lifting up the curl-paper, and placing it, sections lowermost, upon the coating of collodion on the slide. Press on the whole with a piece of dry blotting-paper. The sections adhere to the slide, and the curl-paper is removed. Dry the sections with blotting-paper, and pour over them a layer of thin collodion. They are now permanently fixed, and can be stained on the slide in any way that may be desired. This is an extremely convenient method for serial sections of the central nervous system. XI.-FIXATIVES AND SUBSEQUENT TREATMENT OF SECTIONS. Further Treatment of Sections. This depends on how the sections have been made, and whether they have or have not been previously stained. Paraffin sections must be freed from paraffin. If they are unstained, they must be stained. In most cases it is found advantageous to fix paraffin sections to the slide by means of a "fixative." Many sections can thus be fixed on one slide, and treated simultaneously. The series of events will then be for unstained paraffin sections: (1.) Fixation on a slide. |