Chapter VII: The Celloidin Method 61 



8. Into a small stender dish put chloroform to the depth of 

 3 mm. When a film has formed over the exposed surface of the 

 celloidin place it in the chloroform to harden. It need not be 

 submerged. Keep the vessel tightly covered. The object may 

 be left for a day or two, but 1 to 3 hours usually suffices. 



9. Transfer the block to 70-83 per cent, alcohol, where it 

 may remain indefinitely. 



10. Make a careful study of the microtome used for cutting 

 celloidin (Fig. 32). 



11. Place the block in the object carrier of the microtome at 

 the proper level and arrange the microtome knife obliquely, so 

 that it will slice through the object with a long drawing cut for 

 at least half the length of the blade. If the object is oblong it is 

 advantageous to have the long diameter parallel to the edge of 

 the knife. 



12. Keep both the knife and the object flooded with 70 per 

 cent, alcohol. 



13. Draw the knife through the object with a straight steady 

 pull ; avoid pulling down on or lifting the knife carrier. 



14. If the feed is not automatic push the knife back to position 

 always before turning the screw which raises the object. Cut 

 the sections about 15 or 20 microns thick. 



15. As the sections are cut, transfer them by means of a small 

 soft brush or a paper spatula to a flat stender or a watch-glass 

 containing 70 per cent, alcohol. 



16. Transfer some of the sections through 50 and 35 per cent, 

 alcohol, 2 minutes each, into borax-carmine for from 20 to 30 

 minutes, or until stained (12 to 24 hours) . 



17. Wash successively in 35, 50, and 70 per cent, alcohols, 

 leaving the sections from 2 to 3 minutes in each. 



18. Transfer the sections to 95 per cent, alcohol for 3 to 5 

 minutes. Absolute alcohol is not to be used with celloidin 

 because it dissolves the celloidin. 



19. Clear in carbol-xylol for from 10 to 20 minutes. 



20. Mount in balsam (see chap, vi, I, step 9). 



