272 Modern Microscopy 



of the cube to which the object is to be secured, in order 

 to give the paraffin a better grip upon the wood. The 

 cementing of the paraffin block to the wooden cube is 

 brought about by melting scraps of paiaffin upon the 

 surface of the wood by means of a hot metal instrument ; 

 a small screw-driver will do nicely. While the paraffin 

 upon the wood is still liquid, the block containing the 

 object is just warmed at the base and pressed into contact; 

 subsequently, a heated metal instrument is run around the 

 base of the block to complete the juncture. When the 

 whole has become cold the paraffin block is very carefully 

 squared, and the side which will face the edge of the knife 

 is pared down close to the object — say, within a millimetre 

 or two. Eeference is made to this on p. 274. 



The squaring of the block is easily done by eye after a 

 little practice, or an instrument made for the purpose can 

 be purchased. This is, however, not necessary, for if, 

 when upon the microtome, one side is made perfectly 

 parallel with the knife edge, and the knife is moved to the 

 opposing side, any deviation from the parallel will be easily 

 seen, and can be rectified by a touch of the scalpel. It is 

 not necessary that the two sides of the block at right angles 

 to the knife edge should be perfectly squared. 



Dehydrating. — The following dehydrating apparatus will 

 allow of specimens being passed through the various fluids 

 without being touched, and maintained at any desired 

 distance from the bottom of such fluids : Cut or obtain a 

 piece of stout glass tubing of | inch inside diameter in 2^-inch 

 lengths. Make a small cork ring by means of cork-borers to 

 fit inside the tubing ; take a small circle of washed muslin, 

 place it over the cork ring, and push the whole into the 

 glass tube to the distance required — say, half-way ; procure 

 seven wide-mouthed stoppered bottles of sufficient size to 

 take one of the glass tubes, and the apparatus is complete. 

 Seven bottles are used for the dehydrating and clearing 

 fluids as follows : Alcohols of 30 per cent., 50 per cent., 

 70 per cent., 90 per cent., and absolute, xylol-alcohol, 



