CH. -V] 



COLLODION I\fETHOD 



37 



object, the drops falling about every two seconds. As the sections 

 are cut they are drawn up towards the back of the section knife 

 with a soft brush. They can be kept in order in this way and not 

 interfere with succeeding sections. 



Some operators in drawing the knife across the tissue use a 

 slight sawing motion. However one proceeds, the knife is drawn 

 rather slowly, not rapidly as with paraffin work. 



FIG. 247. Pietzsch microtome^ University of Pennsylvania model. The 

 knife is set very obliquely for collodion sectioning. For paraffin sectioning the 

 knife -Mould be at right angles to the clamp. (Cut loaned by Edward Pen- 

 nock, Philadelphia.') 



If the imbedding was done in a paper box, remove the box 

 and trim the collodion block suitably. Dry the end away from the 

 tissue, wet it with 3% collodion. Use a piece of wood, a cork or 

 other holder of suitable size. Put some 6% collodion on the holder 

 and let it dry for a minute or so, then press the collodion block 

 down on the holder. Leave in the air for a minute or two and 

 then put into 67% alcohol to harden the cementing collodion. 



