EMBEDDING MEDIA. 17 



also be transferred direct from the Alcohol to the cell of 

 Paraffin. In either case the piece is put into the melted 

 Paraffin, which has been poured into a cell, and which has 

 cooled sufficiently to hold the piece in any position required. 

 Another method is to make a hole in a small block of Paraffin, 

 fit in the piece of tissue, and fill up with warmed Paraffin. 



The cell to hold the Paraffin can be made in a variety of 

 ways. A small rectangular tray can be made by folding paper 

 or thin card ; a cylinder can be formed by rolling paper round 

 a cork (allowing the paper to project beyond the cork) and 

 fixing it with a pin run through the paper into the cork. Cells 

 can also be formed by means of two pieces of brass, each of 

 them being bent at right angles, and the cylinders can be cut 

 from brass-tubing. 



When the sections have been cut, the Paraffin can be 

 removed by immersion in Naphtha, Benzol, Toluol, or Xylol, 

 all of which are good solvents of Paraffin. 



For staining, the sections must then be passed through 

 Absolute Alcohol to remove the liquid hydrocarbon. 



Saturation. The piece of tissue, after staining in bulk, is 

 placed in strong Spirit and afterwards in Absolute Alcohol. 

 It is then transferred to Cedar Oil or Xylol, and when cleared 

 is placed in a suitable (not too large) quantity of Paraffin, 

 kept just above the melting point, until the tissue is saturated 

 with it. Both Cedar Oil and Xylol are convenient media, 

 as either mixes readily both with Absolute Alcohol and melted 

 Paraffin. If the pieces of tissue carry much oil into the 

 Paraffin, a second bath of the latter may be used. When the 

 saturation is complete (2 5 hours), the Paraffin should be 

 quickly cooled, and a piece containing the tissue can be cut 

 out with a warmed knife. It is then ready for mounting on 

 the microtome. 



Another Method of Saturation. The tissue after staining is 



c 



