Appendix. 155 



Objects imbedded in paraffin may be cut, by a steady 

 hand, with no other instrument than a sharp razor. Of late 

 years, however, some form of mechanical section-cutter 

 microtome is to be found in every biological laboratory. 

 Such microtomes are the Minot, which is the best for paraf- 

 fin work, and the Thoma, which may be used for paraffin 

 or for celloidin. 



If paraffin has been used as an imbedding mass, the 

 object-holder, metal or wood, is warmed, and the block at- 

 tached by cool water being allowed to run over block and 

 holder until a firm union has been obtained. The position 

 of the object in relation to the cutting-plane of the knife 

 has, of course, been observed. 



Adjust the paraffin block, and cut off thin sections of par- 

 affin until the neighborhood of the object is reached. Trim 

 the remaining portion of the block so that it will be in the 

 form of a cube, the edges of which are parallel to or at right 

 angles with the cutting edge of the knife. Adjusting the 

 gauge so that thin sections of equal thickness will be cut, 

 proceed until as many slices are secured as are needed. 



The following annoyances may arise : 



ist. The sections roll. Correct, by cutting thinner sec- 

 tions, or by using softer paraffin, or by cutting in a warmer 

 room. Sections sometimes roll when the knife is dull. 



2d. As the knife passes through the object, the tissue 

 appears granular and the section porous. - - The trouble is 

 either that the imbedding was not properly done or the 

 knife is not properly sharpened. 



3d. The block at its upper portion becomes white and 

 broken. See if the cutting edge is not set so that it is fur- 

 ther from the block than the back part of the knife. 



4th. The sections crimp, the section of paraffin being 



