222 CLINICAL BACTERIOLOGY AND H&MAtOLDGY 



of the microtome (which must be heated, and the lower sur- 

 face of the block pressed upon it), and the sections cut in the 

 manner described; a very sharp knife is essential, and the 

 stroke must be quicker and sharper than is the case when 

 frozen sections are being cut. In another form of the micro- 

 tome a special inner tube is provided for cutting sections by 

 the paraffin process. The blocks are retained in place by a 

 clamp, and appear in the same position as that occupied by 

 the mass of frozen gum. As the paraffin is not sufficiently 

 hard to be gripped by this clamp, they must first be mounted 

 on a piece of wood of a suitable size and shape. This can be 

 cut out of a piece of firewood, and should have one surface 

 left rough; this surface must be dipped in melted paraffin, 

 and the under surface of the block partially melted in the 

 flame and pressed firmly upon it. The piece of wood is then 



FIG. 43. CLAMP FOR HOLDING WOODEN BLOCK WITH THE PARAFFIN BLOCK. 



to be placed in the jaws of the clamp, and the screw 

 tightened up. 



In the Cambridge Rocker and in some other forms of 

 microtomes the sections adhere to one another at the edges, 

 and form long ribbons as they are cut. In the Cathcart 

 microtome this is not the case, and each section must be 

 dealt \vith separately; it is to be removed carefully from the 

 knife blade with a camers-hair brush or a finely pointed pair 

 of forceps, and placed upon the surface of a bowl of water, 

 just hot enough to soften the paraffin without melting it. 

 When this is done the sections will spread out and lose all 

 the creases, and are then ready to be mounted on slides or 

 cover-glasses. 



It often happens that the sections roll up on the knife. In 

 this case they must be placed on the surface of cold water, 

 and an attempt made to straighten them out by careful brush- 

 ing with a camers-hair brush; when fairly flat they are to be 

 lifted up on a slide or piece of paper (dipped into the water 



