PREPARATION AND STAINING OF TISSUE SECTIONS. 53 



over with the solution of celloidin ; this is applied 

 with a glass rod to the surface which is to receive 

 the piece of tissue. The corks are then set aside 

 for the film of celloidin to harden. The pieces of 

 tissue are allowed to remain in the celloidin solution 

 for from one to twenty- four hours, the time varying 

 according to the structure of the specimen. Better 

 results are obtained in the case of lung, or de- 

 generated broken-down tissue, if left for a much 

 longer time than is found to be sufficient for firmer 

 structures. The specimen, when ready, is removed 

 from the celloidin solution with forceps, and placed 

 upon a prepared cork. A little of the solution, 

 which is of syrupy consistence, is allowed to fall 

 on the piece of tissue to cover it completely, and 

 the mounted specimen is finally placed in 60 to 80 

 per cent, alcohol to harden the celloidin. The 

 specimen will be ready for cutting next day. 



The specimen may be more neatly embedded by 

 fixing it with a pin in a small paper tray, pouring 

 the celloidin solution over it, and then placing the 

 tray in alcohol to harden the celloidin. The em- 

 bedded specimen is then fixed on a cork, which 

 has been cut for the clamp of the microtome. The 

 celloidin in the section disappears in the process of 

 clearing with clove-oil. 



Material infiltrated with paraffin must be cut per- 

 fectly dry, and the sections prevented from rolling 

 up by gentle manipulation with a camel' s-hair 

 brush. They must then be picked off the blade of 



