PREPARATION AND STAINING OF TISSUE SECTIONS. 55 



in water, to wash out the picric acid, and then 

 transferred through weak spirit to absolute alcohol. 

 Ebner's solution also gives excellent results, es- 

 pecially when the structures to be decalcified are 

 placed in fresh solution from time to time. 



(B) METHODS OF EMBEDDING, FIXING, AND 

 CUTTING. 



Material to be cut with the freezing microtome, 

 if hardened in spirit, must be well soaked in water 

 before being frozen ; if hardened in Muller's fluid, 

 it can be frozen at once. 



If Williams' microtome is employed, the hard- 

 ened tissues must first be well soaked in gum 

 mucilage, then frozen, and cut. 



For cutting with Jung's microtome, the tissues 

 are embedded in paraffin, or celloidin, and mounted 

 on cork, or, if firm enough, they may be fixed 

 upon cork without any embedding material at all. 

 Paraffin, dissolved in chloroform, will be found 

 very serviceable as an embedding material, but 

 celloidin is more commonly employed now. The 

 pieces of tissue to be embedded are placed, after 

 the process of hardening is completed, in a mix- 

 ture of ether and alcohol for an hour or more. 

 They are then transferred to a solution of celloidin 

 in equal parts of ether and alcohol, and left there, 

 usually, for several hours. Meanwhile, corks ready 

 cut for the clamp of the microtome are smeared 



