paraffin, and in a solution of gum arable (for the freezing 

 microtome) are hf j re given. It is deemed beyond the scope 

 of these notes to go into the methods for cutting sections; 

 they will be taught in the laboratory. 



Embedding for Cutting with the Freezing Microtome. 



To prepare the tissues for cutting on the freezing 

 microtome, remove the alcohol from the hardened tissues 

 by allowing them to remain in water about eight hours, 

 then transfer to a solution of gum arabic (the solution 

 should be about as thick as syrup). It is made by dissolv- 

 ing the gum arabic in hot water, and straining through a 

 cloth; cool before using. In about six hours they are 

 permeated with the gum arabic and are ready for freezing. 

 Sections need to be cut into warm distilled water, which 

 removes the gum arabic. Before staining or placing in 

 alcohol they must again be washed in distilled water. 



Celloidin or Collodium Embedding.* 



A stock solution of celloidin or collodium is kept on 

 hand. This is made by adding celloidin or collodium to a 

 mixture of equal parts of absolute alcohol and ether until 

 a thick solution is obtained. The stock solution needs to 

 be kept in a well-stoppered bottle, as it thickens on the 

 evaporation of the alcohol and ether. The steps for em- 

 bedding tissues are the following : 



(1) From the 95% alcohol the tissues are placed into 

 absolute for 24 to 48 hours. 



(2) Into a mixture of equal parts of. absolute alcohol 

 and ether from 1 to 2 days. 



(3) Into a thin solution of celloidin, consisting of one 

 part of the stock solution and two parts of the alcohol 

 and ether mixture (equal parts) ; in this they remain, 

 according to the size of the pieces embedded, from 2 or 3 

 days to as many weeks. 



(4) Into the stock solution for an equal length of 

 time. The tissues are ready for further treatment as soon 



* The methods for embedding in celloidin and collodium are 

 the same, and the results seem to the author equally good ; collo- 

 dium is cheaper. The steps here given for the one will answer for 

 the other. 



