3 So 



PREPARATIONS BY THE PARAFFIN METHOD [Ch. XI 



marked out with great clearness in the containing paraffin (see also 



§657)- 



As succeeding sections are cut they push along the previous sec- 

 tions, and if the hardness of the paraffin is adapted to the temperature 

 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, 



B 



Fig. 224. Support of the Microtome Knife so that the Most of the 



Edge Can be Used. 



and if the paraffin block has been properly trimmed at the end the 

 ribbon will be straight and even. If the ribbon is curved sideways 

 it indicates that one side of the block is thicker than the other and the 

 sections are slightly wedge shaped. 



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. 



The thinner the sections the harder should be the paraffin or the 

 cooler the sectioning room ; and the thicker the sections and the larger 

 the object to be cut, the softer can be the paraffin and the higher 

 the temperature. If, then, the sections do not ribbon, make thinner 



