Chapter 



Freezing Method 



The freezing technic tor preparing specimens is unsurpassed in two 

 ways: (1) it is rapid — essential for diagnosis in hospitals; and (2) it can 

 be used for the preparation of sections containing such elements as fats 

 enzymes and some radioscopes that would be lost in alcohol, paraffin 

 solvents or by heat. One disadvantage is that some distortion may be 

 caused by the freezing and cutting. 



Freezing methods formerly used ether, ethyl chloride or other vola- 

 tile liquids. Present methods employ compressed carbon dioxide gas 

 bloAvn into a chamber. There the gas expands, cooling the chamber, 

 and freezing the tissue mounted on it. For this procedure most labora- 

 tories use the clinical microtome with a freezing attachment. An attach- 

 ment also can be used on sliding microtomes, but not, efficiently, on 

 rotary models. There are also dry ice holders available, such as the one 

 manufactured by Fisher Scientific Company — a Dry Ice Freezing Cham- 

 ber. Dry ice is held inside the chamber and the specimen is frozen sim- 

 ply by pushing the dry ice up against the metal top holding the speci- 

 men. Nickerson {1944) fitted the object clamp of a rotary microtome 

 with a small metal box holding dry ice. A new freezing system using 

 Freon is on the market — the Histo-Freeze — a portable freezing vinit, 

 12 X 18 inches, with Freon 12 circulating through the unit (manufac- 

 tured by Scientific Products, Evanston, Illinois). Model 67027A fits 

 American Optical, 67 027 B fits Baiisch and Lomb, and 67 027 C fits the 

 Sartorius freezing microtomes. Lipshaw has a tissue freeze refrigerating 

 unit, counter or desk height, fitting American Optical, Bausch and 

 Lomb, Sartorious or Reichert microtomes. 



02 



