28 PHARMACEUTICAL BOTANY 



3. Take the slide out of the well, wipe off the under side and allow 

 a stream of 95 per cent, alcohol to run over the upper side from a 

 pipette. 



4. Place the slide upright in a well of safranin for from four to 

 twenty-four hours. 



5. Take the slide out of the safranin well and extract excess of 

 stain with 57 per cent, alcohol. 



6. Place the slide in a well of gentian violet or methyl-green for a 

 second or more. The time varies for different objects and can only 

 be determined by trial. 



7. Rinse slide with 70 per cent, alcohol from pipette. 



8. Pour absolute alcohol over sections, follow with a few drops of 

 clove oil, replace clove oil with cedar oil. 



9. Mount in balsam. 



10. Label slide. 



IMBEDDING IN CELLOIDIN 



Whenever material is unsuited for free hand sectioning and will 

 not give good results when imbedded in paraffine on account of size, 

 hardness, or brittleness, celloidin may be resorted to as an imbedding 

 medium. 



The technique employed is similar to that of the paraffine method 

 so far as the preliminary fixing, hardening and dehydrating are con- 

 cerned up to and including the 95 per cent, alcohol stage. From this 

 point the various succeeding steps in the procedure are as follows: 



1. Place material in equal parts of 95 per cent, alcohol and ether 

 (known as ether-alcohol) for several hours. 



2. Transfer to a 2 per cent, solution of celloidin in ether-alcohol, 

 for 2-5 days. 



3. Transfer to a 6 per cent, solution of celloidin in ether-alcohol, 

 for 2-5 days. 



4. Transfer to a 12 per cent, solution of celloidin in ether-alcohol, 

 for 3-10 days. 



5. Prepare a pine block sufficiently large in cross section to sup- 

 port the material and otherwise adapted to its being clamped in the 

 object carrier of the microtome. Soak one end of this block in 



