140 Microscopic Histochemistry 



cutting and to disintegrate when floated on water. The reni- 

 edy is infiltration of the blocks with thin celloidin before 

 paraffin-embedding. 



The temperature of the paraffin oven should not exceed 

 56° C, and the tissues should not be exposed to this tem- 

 perature for longer than IM hours. Embedding can be has- 

 tened by the use of reduced pressure.* A piece of rubber 

 tubing, connected through a safety bottle to a water pump 

 and introduced into the oven through its ventilating opening, 

 will serve as a simple suction apparatus. The melted paraffin 

 is kept in a wide-mouthed bottle which has a tight-fitting 

 stopper, with a piece of glass tubing in its single perforation. 

 The end of the rubber tubing is attached to the glass. The 

 bulk of benzene or chloroform is removed by the first change 

 of paraffin in an open dish (about 15-20 minutes). The 

 pieces are now transferred to the suction bottle, and the 

 vacuum is turned on gradually. Bubbling, quite lively at the 

 start, soon decreases and ceases altogether in about 30 min- 

 utes. A third change of paraffin in an open dish (about 10- 

 15 minutes) completes infiltration, and the pieces are then 

 ready to be embedded. 



The following schedule of fixation and embedding is sug^ 

 gested for all enzymes unless otherwise specified in the text: 



1. Chill tissue for 15-30 minutes in the icebox. Fix shoes 

 not thicker than 3 mm. in chilled acetone for 24 hours. It is 

 advisable to trim the pieces even thinner with a razor blade 

 as soon as they have gained some consistency (2-3 hours). 



2. Dehydrate in two or three changes of absolute acetone 

 or alcohol, about 12 hours each. 



3. Transfer pieces to a mixture of equal volumes of alcohol 

 and ether for a few hours. 



4. Transfer to a 2-3 per cent solution of celloidin (collo- 

 dion, U.S.P., diluted with ^A to 1 volume of alcohol-ether 

 mixture) for 12-24 hours. 



5. Drain pieces rapidly and carry them through two 

 changes of chloroform, 32-1 hour each. ^ 



4. Gomori, G.: Am. J. CHn. Path., 16:347, 1946. 



