MYELON

CHAPTER XL.
MYELON.
559. Central Nervous System (Betz's methods').
HARDENING.
The spinal cord, medulla oblongata, and pons Varolii are
treated as follows :-The dura mater is removed, and they are
hung up in a cylinder containing 75 to 80 per cent. alcohol,
to which is added enough iodine to produce a light-brown
colouration. After from one to three days the preparation
will be found to be somewhat surface-hardened; it is taken
down and the pia mater and arachnoid are removed. If the
pia mater does not come away completely enough the prepa-
ration is put back for some days into the alcoholic iodine.
The membranes having been removed, the preparation is put
back into the original fluid, which is found to have become
colourless owing to absorption of the iodine by the tissues.
Fresh quantities of a strong solution of iodine in alcohol are
from time to time added to the liquid in order to keep it at
its original strength of iodine (as shown by the colour). If
the membranes have been carefully removed it will be found
that after about six days the preparation ceases to take up
further quantities of iodine. The preliminary hardening may
now be considered complete.
The preparation is now brought into a 3 per cent. solution
of bichromate of potash. (A small weight is attached to it to
prevent any portion of it from floating above the surface of
I 'Arch. Mik. Anat.,' ix (1873), p. 101 ff.

347