EMBEDDING MEDIA. 15 



Method of Using. 

 Before using either of the above for embedding, the tissues 

 must be washed for several hours in frequent changes of 

 Water, to free them from Alcohol, and then placed for 24 hours 

 (preferably 3 or 4 days) in the Gum or Gum and Syrup, to 

 saturate them before freezing on the microtome. 



(iii.) CELLOIDIN. 



Celloidin dissolved in equal parts of Absolute Alcohol and 

 Ether, an 8 p. c. Solution being used for Thick Celloidin, 

 and diluted with an equal volume of the Ether- Alcohol for 

 Thin Celloidin. 



Method of Using. 



The tissues (previously hardened by one of the methods 

 already given), if not already in strong Alcohol, should be 

 placed there ; they are then immersed for 12 hours in equal 

 parts of Absolute Alcohol and Ether. After this they are 

 immersed in Thin Celloidin for 24 hours ; then for another 24 

 hours (preferably 2 or 3 days) in Thick Celloidin, so that it 

 may thoroughly permeate the tissues. The pieces are now 

 removed from the solution, and placed on small cubes of soft 

 wood, care being taken to see that the wood is quite dry. 

 Allow the Celloidin to harden for a few minutes, and then 

 place the wood with the tissue in 90 p. c. Alcohol for 12 to 24 

 hours. They are then ready for clamping in the microtome. 



If material, saturated with Celloidin, is to be cut on the 

 freezing microtome, the piece when removed from the Thick 

 Celloidin, is placed with some of the Celloidin in a small paper 

 case. Allow a thin film to form on the surface by evaporation, 

 and then place the paper case with contents into 80 or 90 p. c. 

 Alcohol for 12 to 24 hours or longer to harden. When it 

 assumes the consistency of soft cheese take it out of the 

 Alcohol, remove the paper case, and place it in Water to wash 



