24 



EXERCISES IX THE PREPARATION OF TISSUES. 



is caused to make up and down strokes. The latter movement cuts 

 the section by carrying the block across the razor edge, the spring 

 D supplying the force. The block is moved forwards for each suc- 

 ceeding section by tilting the rest E razorwards. The tilting is 

 accomplished by turning the screw F, which raises that end of the 

 rest. F is rotated by a catch G on the lever C which engages the 

 teeth on the large disc of F. The catch G carries a pin which 

 projects downwards and rests against a sector H. The latter controls 

 the position of the catch so that it passes clear of the disc during 



FIG. 



Rocking Microtome (modified), see text. A' additional 

 block-holder (Durham). 



the cutting of the section, i.e., down stroke of the block A, and 

 also during its up stroke until A has passed clear of the razor. 

 The thickness of the section is fixed by the number of teeth through 

 which the disc on F is moved and this again is determined by the 

 relative position of H which controls the catch G (each tooth equals 

 a thickness of 4 //,). Adjustments are provided for regulating (1) the 

 thickness of the section, (2) the excursions of the rocking arm, and 

 (3) the position of the razor. 



In the original form of this excellent instrument, the razor is 

 carried in a fixed support. The movable carrier illustrated above 

 allows, without loss of rigidity, of great freedom of orientation in 

 two directions, whilst the third direction is obtained by turning the 

 brass thimble itself. This modification, together with the adjusting 



