148 



The Preparation of Microscope Slides 



Fig. 112. Starting the paraffin ribbon. 



Fig. 112 is completely tight. The set screws holding the block holder may 

 be tightened in any order, provided that the result leaves the block cor- 

 rectly orientated, but those connected with the knife must be done in the 

 correct order. First the knife is inserted into the holder and fixed firmly 

 but not tightly in place by the two bearings at each end. The tightening 

 of these screws causes the two movable holding arms to hold the knife 

 near its edge. The knife is held in a pair of hemicylinders, which may be 

 moved to adjust the knife angle (see Fig. 108). The knife should be set 

 at the angle that experience has shown to be desirable— no guide other 

 than experience can be used— and the two set screws that lock these in- 

 clinable hemicylinders in place then tightened. While the knife is held in 

 place, the two original set screws should be screwed as tightly as the 

 thumb can bear. This leaves the two set screws, which come through the 

 inclinable hemicylinders and bear on the back of the knife. These two set 

 screws should be tightened simultaneously and uniformly. The effect of 



