CH.XI] PREPARATIONS BY THE COLLODION METHOD 389 



least once. The used chloroform will contain some ether alcohol, 

 but is good for killing animals. 



After 24 or 48 hours the collodion should be firm all through. Then 

 it is placed in 67 % alcohol where it may be left a day or more. If it is 

 to be left an indefinite timethe67 % alcohol should be changed for 82 %. 



§ 632. Sectioning by the collodion method. — For this one can use 

 a table microtome or one of the sliding microtomes. The sections 

 are made with a knife set obliquely and hence with a drawing cut. 



Fig. 233. Perforated Section Lifter for Handling Single Collodion or 



Frozen Sections. 



The holder with the small piece of tissue is clamped in the micro- 

 tome and arranged as desired; then the sections are made with an 

 oblique knife which is kept wet with 82% alcohol. The best way 

 to keep the knife wet is to have a dropping bottle over the object, 

 the drops faUing 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 parafl&n work. 



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 



