112 



ALEXANDER L. DOUNCE 



Space for 

 acetone-dry ice 



To pump 



Condensing 

 surface 



Fig. 3. Schematic drawing of one type of apparatus for lyophilizing tissue. If a 

 large apparatus of this sort is used, the construction should be of metal, since glass 

 may shatter. (0.2 times actual size.) 



crystalline catalase suspended in water can be frozen and lyophilized with- 

 out apparent damage if the flasks are surround by a bath of ice and water, 

 whereas, if the flasks are surrounded by air, damage is caused.^^ 



To cool the traps in which water is frozen out, acetone-dry ice mixtures 

 may conveniently be used. However, if diffusible substrates are to be 

 studied, the use of liquid nitrogen is recommended for this purpose and 

 as low a temperature as possible should be maintained in the bath surround- 

 ing the flasks which contain the tissue. How low this temperature can be 

 \vithout slowing the lyophilization to a negligible speed is not known. 



One type of lyophilizer which has the advantage of a very short path 

 from the tissue to the freezing-out trap is shown in Fig. 3. This apparatus 

 unfortunately has the disadvantage that it is difficult to surround the flasks 

 containing the tissue with cooling baths. The type of apparatus shown in 

 Fig. 4 has been used with considerable success in the reviewer's laboratory. 

 It is included here mainly for the benefit of those who are not expert in 

 freeze-dry techniques. The path between the material being dried and the 

 first flask is kept as wide as possible. (Note especially the large-bore stop- 

 cock.) Ordinary Dewar flasks are used to hold the mixture of acetone and 

 dry ice which is used for cooling, but a metal container should be used to 

 hold the ice and water surrounding the centrifuge bottles, since a Dewar 

 flask may explode if a solid block of ice is formed in it during the course 

 of the lyophilization. It is desirable to tape the Dewar flasks and to place 



'' A. L. Dounce and R. R. Schwalenberg, Science 111, 654 (1950). 



