274 Modern Microscopy 



the paraffin and the thickness of the sections required. If 

 the paraffin is too soft for the temperature of the work- 

 room and thickness of sections, then the sections will 

 probably crumple together ; if the paraffin is too hard, 

 then the sections will curl or roll upon the knife. A little 

 rolling, however, of the first few sections is of no impor- 

 tance ; as the first two or three are cut, they should be 

 unrolled by the aid of two ' crow-quill ' sable hair-brushes 

 slightly moistened in the lips, then, other matters being 

 favourable, the ribbon of sections will come away satisfac- 

 torily. You may cut a ribbon of sections without the 

 slightest curling, when isolated sections cut at the same 

 time and under the same conditions will curl beyond hope. 



Cutting Sections.— In the remarks that follow upon 

 cutting, we shall presume that the Schanze microtome 

 (Fig. 65) is being used. The space at command does not 

 admit of entering further into the working of the various 

 instruments previously described, so that the remarks must 

 be confined to one, although applicable to any. 



In the first place, the Henking knife must be secured 

 square with the tramway ; this is easily brought about by 

 having a few lines scratched upon the upper surface of the 

 knife-carrier at right angles to its direction of movement. 

 The handle of the knife can then be made to coincide with 

 one of the lines ; the blade will then be sufficiently square 

 for practical purposes. The object has to be orientated 

 into correct position. If the object has to be exactly 

 vertical to the direction of the knife movement, first square 

 the object by eye with one of the vertical fittings upon the 

 body of the microtome. It may then be squared in the 

 other direction by placing the edge of the knife immediately 

 over the object and close to it, and examining the reflection 

 of the object upon the under surface of the knife. When 

 the object and its reflection form a straight line, the object 

 must be plumb. Orientating operations are facilitated 

 by the free use of the long lever-arm, which moves the 

 object rapidly in a vertical direction without giving need- 



