49 



(ii) Fold a piece of paper, so that by folding 

 a trough of required size is made. If an extra 

 length of paper be left at each end of the trough 

 it can be folded down and holds the rest in posi- 

 tion. Fill with freshly melted paraffin and 

 add the piece of tissue picked up with warmed 

 forceps. 



(iii) Use metal pieces, supplied with most 

 microtomes, upon a slab of glass. 



The following points should be borne in 

 mind : — 



(i) Fresh paraffin should be melted for the 

 block, as paraffin frequently melted, or kept melted 

 for long periods, does not form so uniform a mass 

 when cooled as freshly melted paraffin. 



(ii) The more rapidly the paraffin is cooled, 

 the more uniform is the resulting mass. It is well 

 therefore, as soon as a well-marked surface crust 

 appears, to plurlge the watch glass or trough into 

 cold water. 



When cold, cut out a square block with the 

 tissue arranged in the position required for the 

 sections. 



5. Cut sections. 

 Note (i) The angle the knife is placed at is 

 important, and must be found by experience. 



(ii) It is well to use pads of paper to protect 

 the edge of the razor, where it presses against the 

 iron of the microtome. 



(iii) To cut in ribbons, the top and bottom 

 edges of the block must be parallel and horizontal. 

 It is well to dip the block in soft paraffin, or 

 merely to smear the top and bottom surfaces of 

 the block with soft melted paraffin. 



E 



