56 



PRACTICAL HISTOLOGY 



[VII 



backwards and forwards the guard of the catch, the position of 

 this determines how far the wheel is pushed round by the catch, 

 i.e. the thickness of the section. Pull the handle forward, and 

 then slowly move it back, counting the clicks of the catch as it 

 passes over the teeth of the milling ; adjust the guard so that 

 there are 8 to 10 clicks. Eight teeth give sections approximately 

 5 p. in thickness. 



Fig. 3. 



Procedure. Imbed the tissue as in 5, and shape the paraffin 

 into a rectangular block. Take the paraffin carrier from the 

 microtome. On this fix the imbedded tissue, thoroughly melting 

 the adjoining surfaces of the paraffin by means of a heated knife. 

 With a sharp scalpel, carefully shape the part of the block sur- 

 rounding the tissue so that the surface to be cut is rectangular. 



Screw the large screw of the microtome downwards as far as 

 it will go. Fix the carrier to the microtome, adjusting it so that 

 the paraffin reaches nearly up to the position to be taken by the 

 razor. Fix the razor firmly in the frame. Leave the right arm 

 on the end of the lever carrying the paraffin so as to bring the 

 paraffin on a level with the edge of the razor. Adjust the paraffin 

 carrier so that one edge of the block to be cut is parallel to the 

 edge of the razor and about half a millimetre from it ; in doing 



