HORSE-SHOE AND ROCKING MICROTOMES. 



23 



the frame adds steadiness. As the frame is carried back for the next 

 stroke the regulating screw is turned clockwise through a small 

 fraction of a turn by the fingers which grasp it, this lowers the razor 

 edge and determines the thickness of the next section. By keeping 



FK;. 8. Method of using the horse-shoe microtome. 



the wrists firmly upon the table the same part of the razor edge 

 is used at each successive cut, a matter of importance, as the 

 edge is generally curved, and lateral displacement would vary the 

 thickness. Short ribbons of six or seven sections adhering to each 

 other may be cut. 



Imperfect embedding, causing want of homogeneity, and grittiness in 

 cutting, is due to imperfect removal of water and alcohol in the substitution 

 processes, and can only be cured by retrograding through the successive 

 steps to alcohol and back again to paraffin. 



Blocks and sections can be preserved in pill boxes for later use. 



Rocking- microtome. (Cambridge Instruments Company.) This 

 instrument cuts ribbons, i.e.. successive sections adhere to each other. 

 The block of paraffin containing the tissue which is to be cut is 

 fastened to a brass thimble by means of a hot wire, and its front 

 and back edges are pared straight and parallel to each other. Slip 

 the thimble A into position on the end of the rocking arm B. 

 From the other end of B a cord passes from a clamping ring over 

 guide pulleys to the lever C. By the to and fro movement of C, A 



