Alfcrofome Sectioning of Material in Paraffin 41 



Metal mounting disks (Fig. 6.1 B) afford greater rigidity than 

 plastic blocks and are indispensable for cutting very thin sections, 

 or for sectioning large pieces of firm material. Disks remain cold 

 longer after chilling, thereby keeping the paraffin block cold for 

 sectioning. Disks are much more expensive than homemade blocks, 

 and most laboratories have a limited supply, making them unsuitable 

 for the routine sampling method described above. Some microtomes 

 have a built-in tissue-mounting disk on a ball-and-socket joint. This 

 device is satisfactory for work in which each piece of material is used 

 up at one cutting, thus emptying the carrier for the next piece or for 

 the use of other workers. For class use or for work requiring much 

 sampling of diverse materials by several workers, removable disks 

 or blocks are much more desirable. 



To fasten a piece of material on a mounting block, trim the 

 paraffin around the material so that the cutting plane is established. 



Fig. 6.1 — Mounting of tissues on object blocks: A. wood or plastic block with scored 

 surface; B, metal object disk; C. method of orienting paraffin block and fastening 



to object block. 



Lay the cutting face on a clean surface. Heat the mounting block, 

 press it firmly on the back of the specimen, and hold in contact 

 until the wax cools (Fig. 6.1 C) . Build up a fillet of paraffin around 

 the specimen to afford firm l^racing for the tissues (Fig. 6.2) . Cool 

 thoroughly before sectioning. 



Some workers of acknowledged skill use a heavy knife for class- 

 work, for routine preparation of teaching material, and for research. 

 Other workers of equal ability use either a knife or a razor blade in 

 accordance with requirements of the work in hand. For sections 

 ranging from 8 to 15 [.i in thickness, a sharp razor blade in a suitable, 

 rigid holder will match the work of the heavy knife. The thick 

 type of razor blade (Enders or Christy) can be stropped, used 

 repeatedly, and discarded when stropping no longer restores the 

 edge. In a course in microtechnique, for the routine preparation 



