xxxii INTRODUCTION. 



allowed to rise above 60° C. Paraffin melting at 55° or 56° C. 

 is the best, though a softer paraffin may be used in a cold 

 room, if it be found that the hard paraffin crumbles befo^-e 

 the razor. When the object is thoroughly permeated, rf '~» 

 transferred to a small trough of paper with just enoi^?h 

 paraffin to form on cooling a block completely enclosing it. 

 It must be cooled as quickly as possible by placing the trough 

 in a dish containing cold water, as the paraffin is liable ro 

 crystallise if allowed to cool slowly. A couple of L-shaj 'd 

 blocks of metal, resting on a plate of glass or metal so as 

 form a box of adjustable size, may be used in the place of the 

 paper trough. The block containing the object is fixed Ji 

 the microtome ; the most efficient of all contrivances for tb' s 

 purpose is, perhaps, a grooved metal plate which is simp 7 

 warmed slightly and pressed against the end of the block, and 

 then cooled quickly as soon as the block has begun to melt. 

 The further procedure depends entirely upon the particular 

 microtome used. The sections are to be mounted as described 

 in section XI. 



XI. ON MOUNTING MICEOSCOPICAL OBJECTS. 



The most convenient slide for microscopical objects is a 

 slip of glass three inches long and one inch wide, or for large 

 series of sections the slide may be 1^ inch wide. The glass 

 should be free from air-spaces and other flaws, and the edges 

 should be ground. 



Cover-glasses must be very thin (No. 1) and free from 

 flaws. For single objects square covers (i to | inch) are 

 best, and for series of sections oblong covers, which should 

 not come within ^V inch of the edge of the slide; space should 

 alFo be left at one end for a label. 



' Cells ■ are required to protect thick objects from the 

 pressure of the cover-glass. Thin flat rings of tin are good, 

 and should be cemented to the slide with gold size or ' brown 

 cement ; ■ or a ring of the cement painted on with a brush 

 and allowed to dry may be used as a cell for thinner objects. 



