1 6 Neurological Technique 



H. The graded alcohols. — Absolute, 95 per cent., 70 per cent., 

 50 per cent., 35 per cent. See formula and table, p. 21. 



PROCEDURE. 



1. To fix, place ganglia or small pieces of spinal cord or 

 brain (5 mm. thick) in a quantity of Van Gehuchten's fluid (A) 

 about twenty times the volume of the tissue for 3-12 hours. The 

 vessel should be tightly closed during the period of fixation. 



2. To wash and dehydrate, transfer the tissue direct from the 

 fixing fluid to 10 to 15 volumes of absolute alcohol for 2-6 hours. 

 During this period the absolute alcohol should be changed two 

 or three times. 



3. To clear, place the tissue in about 10 volumes of the 

 clearing fluid (E), J^-2 hours. 



Note. — Pure xylol will do for clearing, but usually takes a longer time 

 than the mixture. When cleared, the tissue appears slightly translucent 

 instead of white, as when first transferred from the alcohol. In all cases it is 

 better to remove the tissue from the action of the oils as soon as it is thor- 

 oughly cleared. The clearing may be hastened by agitating gently from 

 time to time and by slightly warming (40° C). All the histological processes 

 which, like dehydration, clearing, staining, etc., depend upon diffusion, may 

 be accelerated with a rise in temperature and by an agitation of the fluid 

 about the specimen. By means of diffusion one liquid replaces another 

 within the tissue. 



4. To imbed in paraffin. — (a) From the clearing fluid trans- 

 fer the tissue to a covered watch-glass or paraffin bath-pan con- 

 taining about 5 volumes of melted soft paraffin (melting point 

 about 45° C.) for 20-30 minutes. The paraffin bath must have 

 been previously prepared and raised to the melting temperature 

 of the paraffin. 



(b) Transfer from soft paraffin to an equal amount of hard 

 paraffin (melting point about 55° C.) for 40-60 minutes. See to 

 it that the melting point of the paraffin is maintained, but not 

 exceeded. 



(c) To imbed, with warmed forceps transfer the pieces of tis- 

 sue to watch-glasses or (preferably) paper boxes, containing hard 

 paraffin which is kept melted by working with watch-glasses or 



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