Chapter V: The Paraffin Method 41 



the paraffin block after a section has been cut. If the knife has 

 a flat under surface it requires more tilt than if the surface is 

 hollow ground. For a flat under surface the tilt should be about 

 9 degrees from the perpendicular. See that the knife is held 

 firmly in place. 



Caution. The knife should be kept in its case when not in 

 the machine. The edge is very easily injured. 



13. Set the regulator so that the microtome will cut sections 

 about 10 microns thick. A micron is one-thousandth of a milli- 

 meter. 



14. Unloose the catch which locks the wheel and revolve the 

 wheel with the right hand. A few revolutions should bring the 

 block of paraffin into contact with the knife. As each new section 

 is cut, it displaces the last one and if the paraffin is of the proper 

 consistency unites by one edge with the displaced section. Thus 

 a ribbon or chain is formed. When the ribbon becomes of suffi- 

 cient length support the free end by means of a hair brush held 

 in the left hand. To prevent breaking the ribbon avoid pulling 

 it taut. A silk carrier for it may be attached to the machine but 

 there is little need for such after one has acquired a little skill in 

 supporting it. 



Caution. Never bring a needle or other hard object near the 

 edge of the knife. If the paraffin does not ribbon properly con- 

 sult the table at the end of this chapter. 



15. When a sufficient number of sections have been cut, care- 

 fully place the ribbon on a piece of paper. Protect it from 

 draughts of air which will carry away or disarrange the sections. 



16. Cut the ribbon into strips of such length that they may be 

 placed in successive rows one above the other under the cover- 

 glass that is to be used. Mark out on a sheet of paper the 

 exact size of the cover-glass so that there can be no mistake in 

 cutting strips of the proper length. A margin of 2 or 3 mm. 

 should be allowed for the cover. 



17. Place a small drop of albumen fixative on a clean glass 

 slide (for cleaning see memorandum 14, chap, vi), and spread it 

 evenly over the surface, except the end which is to bear the label 



