108 CLINICAL BACTERIOLOGY AND H.EMATOLOGY 



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

 tightened up. 



In the Cambridge Rocker and in some other forms of micro- 

 tomes 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 with separately ; it 

 is to be removed carefully from the knife blade with a camel's- 



FiG. 38. — Clamp for holding Wooden Block with the Paraffin Block. 



hair brush or a finely pointed pair of forceps, and placed upon 

 the surface of a bowl of water, just hot enough to warm 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 brushing with a 

 camel's-hair brush ; when fairly flat they are to be lifted up on 

 a slide or piece of paper (dipped into the water and insinuated 

 below them), and transferred to the hot water as before. But 

 the rolling of the sections may often be prevented by sharpening 

 the knife, by re-embedding the tissues in harder or in softer 

 paraffin according to the weather, or by varying the angle which 

 the knife edge makes with the glass runners of the microtome. 

 These devices can only be learnt by experience. 



When the sections are flattened out on the surface of the hot 



