CUTTING SECTIONS. 



59 



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 i 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 ngainst 

 the knife, by means of a camel's-hair brush. Several section- 

 flatteners attached to the cutting-knife have been used for this 

 purpose. Take a wire i 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 



