Production of Sections 275 



less wear to the micrometer screw. Having arranged the 

 orientation, the two surfaces of the paraffin-block must be 

 brought absolutely parallel to the knife-edge, as previously 

 mentioned (p. 271). A lens will be found of great assistance 

 in this operation, especially if it can be supported over the 

 object so as to leave both hands free. The knife-block 

 with knife attached should now be removed from its guides, 

 in order that the tramway may receive a little oil. One 

 drop of sperm-oil should be rubbed over the three raised 

 surfaces, and then wiped off with a wash-leather kept for 

 the purpose. Oil in quantity or dust upon the slides will 

 give no end of trouble. The micrometer screw and the 

 focusing apparatus, described on page 246, should now be 

 adjusted, and everything is ready for cutting. If the em- 

 bedding has been performed in the manner recommended 

 (p. 268), there will probably be a slight thickness of wax 

 to be cut through before the object is reached. This is an 

 advantage, as it allows a ribbon to be fairly started before 

 the object is cut into. 



In manipulation by hand, the knife-carrier is lightly but 

 firmly held before and behind, by the thumb and forefingers, 

 and moved gently, but rather quickly, to and fro. The knife 

 need not be made to travel the whole length of the tram- 

 way, two inches or so in front of the object to half an inch 

 beyond will be sufficient. Previous to the advance of the 

 knife, pull the focusing-lever towards you so as to raise 

 the object the required distance. In releasing the focusing- 

 lever, do not let it run back so as to strike the stop-pin 

 a smart blow, but guide it back with the hand, otherwise 

 tremor will be imparted to the whole microtome, to the 

 detriment of the sections, especially to the very thin ones. 

 As previously mentioned, the few first sections will probably 

 curl upon the knife ; they may be unrolled in the manner 

 indicated (p. 274). If they cannot be unrolled they must be 

 removed, the knife-edge carefully cleaned, and another 

 start made.* The cleaning of the knife-edge is easily 



* Curling upon the knife is in consequence of the paraffin being too 

 hard for the thickness of sections. To remedy this, cut thinner 



18—2 



