CH. A'] 



COLLODION METHOD 



3°7 



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 would 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. 



