296 



PARAFFIN METHOD 



\_CH. X 



The knife edge meets the paraffin squarely as in planing. The 

 thickness of section is provided for in the automatic microtome by 

 the indicator which may be set for any desired thickness, or one can 

 turn up the screw by hand in the table microtome. (Fig. 229). 

 The paraffin and its contained tissue are cut in a thin shaving. If 

 the tissue was stained in toto with eosin as suggested in 440 A, it 

 is marked out with great clearness in the containing paraffin. 



As succeeding sections are cut they push along the previous 

 sections, and if the hardness of the paraffin is adapted to the tem- 

 perature where the sectioning is done the edges of the successive 

 sections will be soldered as they strike. This produces a ribbon as 

 it is called, and if the paraffin block has been properly trimmed at 

 the end the ribbon will be straight and even (Fig. 234). If the rib- 

 bon is curved sideways it indicates that one side of the block is 

 thicker than the other and the sections are slightly wedge shaped. 



FIG. 234. Automatic rotary microtome for paraffin sectioning. Sections 

 from if.i to ioot-1 may be cut on this instrument. (Cut loaned by the Spencet 

 Lens Co.) 



If the paraffin is too hard for the room temperature and for a 

 given thickness of section the sections will curl ; if it is too soft the 

 sections will crumple. 



