Method XII yj 



5. Transfer from water to 70 per cent, alcohol, changed two 

 or three times, 4—12 hours. 



6. To dehydrate, transfer to 6-8 volumes of 95 per cent, alco- 

 hol for I hour. 



Then replace 95 per cent, with an equal quantity of 97 per 

 cent, alcohol (equal parts 95 per cent, and absolute) for 1-2 

 hours. 



Pure absolute alcohol had better be avoided, since the mye- 

 line of the sheaths sometimes shows indications of having been 

 partially dissolved by it. For the same reason cedar oil or clove 

 oil must be avoided in the clearing. 



7. To clear, transfer the pieces from 97 per cent, alcohol to 

 8-10 volumes of the carbol-xylol (C) for 1-4 hours, then place in 

 pure xylol for y^ hour. Pure xylol is a better vehicle for the 

 paraffin. 



8. Imbed in paraffin as in I, 4, p. 16. 



9. Mount the block in position to make sections in the 

 required plane (usually transverse to the fibers) and make thick 

 sections — 1 5-20 /l*. 



10. The sections may be fastened to the slide by the dry 

 method (III, 14, p. 28). Arrange the sections serially. 



11. To mount, dissolve off paraffin in xylol, 20-30 minutes, 

 and mount in balsam (see I, 16, p. 19). 



When cut transversely, the degenerating fibers appear as 

 black, granular spots, while all the other structures appear as a 

 light yellow. 



If it is merely desired to follow a degenerating tract, and if 

 that tract is large, the material may be imbedded in celloidin 

 and sectioned as in X, 3, 4, and 5, p. 64. If, however, it is 

 desired to study thesprocesses of degeneration, and especially if 

 the degeneration is slight, to imbed in celloidin would involve 

 risk, since both the ether-alcohol and the absolute alcohol 

 equired in the celloidin method may have a dissolving effect 

 upon the medullary sheaths. 



When material from the central nervous system has been 

 imbedded in celloidin, time and trouble may be saved in making 



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