CH. VIZ.] PARAFFIN SECTIONING. 165 



from one to three days. (Any other good method for fixing and hard- 

 ening the elements may be used, only the special conditions necessary 

 for the reagent must be observed. The time might be longer or shorter 

 than for picric-alcohol.) 



After the tissue is properly fixed and hardened in, pour off the 

 fixative and add 67 ( /o alcohol. Leave this on the tissue from 1 to 3 

 days. 



Pour off the 67 % alcohol and add 82 % alcohol. Leave this on the 

 tissue at least 1 day. The tissue may remain indefinitely in 82% alco- 

 hol. 



§ 270. Dehydration and Preparation for Imbedding. — From the 

 pieces of tissue fixed and hardened, cut pieces 5 to 10 millimeters long 

 and 2 to 3 millimeters in diameter and dehydrate them one day in 95 % 

 or stronger alcohol using a preparation vial (Fig. 130). Leave the 

 stock tissue in the 82% alcohol. If one changes the 95% alcohol after 

 3 or 4 hours and adds fresh 95 % the pieces of tissue of the size here 

 given will be sufficiently dehydrated in 5 or 6 hours. Larger pieces 

 require more time. 



(If one is studying organs then the whole organ may need to be pre- 

 pared for imbedding, but for the minute structure small pieces are 

 preferable as thinner sections may be made. ) 



§ 271. Saturating with Chloroform. — After dehydration pour off 

 the 95 % alcohol and add pure chloroform. The chloroform will re- 

 place the alcohol in a few hours. It will do no harm to leave the tissue 

 in chloroform a day or more. Small pieces are usually sufficiently pene- 

 trated in 4 to 6 hours. 



§ 272. Infiltrating with Chloroform Paraffin. — Place the tissue 

 from the chloroform into chloroform paraffin (§ 301) using a tin dish 

 (pattie dish). Place the dish into the paraffin oven where the paraffin 

 will remain melted. The tissue being full of chloroform will allow the 

 penetration of the chloroform paraffin, and the heat will drive off the 

 chloroform so that after 3 to 5 days with small objects and a small 

 amount of chloroform paraffin, the chloroform will have evaporated 

 and the tissue will be infiltrated with pure paraffin. It is possible to 

 hasten the infiltration by pouring off the chloroform paraffin on the 

 second day and adding pure paraffin, but the high temperature neces- 

 sary for keeping the pure paraffin melted is injurious to many tissues. 



§ 273. Imbedding in Pure Paraffin. — After the chloroform has 

 evaporated the tissue should be imbedded. One can tell whether the 

 chloroform has all been driven off by tasting the paraffin, It will have 

 the sweetish taste of chloroform if any is present. If any is present 



