VIII. HISTOLOGY OF NERVE TISSUES 
A. NERVE CELLS (NEURONES). 
i. Smear preparations of gray nerve substance from the spina 
cord. These are made by applying to a clean cover-slip by means 
of the point of a scalpel, a bit of the gray matter from the freshly 
exposed ventral region of the spinal cord of a recently killed 
mammal . 1 Remove the cover-slip with the adhering nerve sub¬ 
stance, place this in contact with another cover-slip, press the two 
tightly together and then separate them by sliding them apart, 
thereby spreading the nerve substance in a thin film over the 
surface of each glass. Dry these smears by holding each carefully 
in a pair of forceps and passing it three or four times, film side up, 
through an alcohol flame, allowing a few seconds to elapse between 
each two successive exposures to the flame. When the film is dry, 
stain it in a dilute aqueous solution of methylene blue by gently 
floating the cover-slip, film down, upon the surface of the stain, 
which may be conveniently used in a watch glass. The process 
of staining should be continued until a deep purple color is 
imparted to the film. Rinse in water, dry off the excess of water 
with filter paper, being careful not to touch the film, and lay the 
preparations aside with the film up until thoroughly dry. Clear 
by floating each cover-slip, film down, in a watch crystal of xylol. 
Place a drop of balsam on the middle of a clean slide and after 
carefully removing the excess of xylol from the film, place the 
cover-slip, film down, upon the balsam. 
Examine under low power, and amid the general debris look 
for large, branched nerve cells. Move the slide so as to bring one 
of these into the center of the field and apply the high power. 
Note the nucleated cell body or perikaryon; the numerous deeply 
stained tigroid bodies (Nissl corpuscles) and delicate neuro-fibrillse 
in the cytoplasm; the paler nucleus, often irregular in outline 
1 Material obtained from a market often proves excellent, even after it has 
been frozen. 
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