90           THE MICROTOMIST'S VADE-MECUM
CHAPTER      XI.
GOLD CHLORIDE.
109. Gold Chloride (Cohnheim's methodl).-The well-known
"gold method " was invented by Cohnheim. He practised it
as follows: Fresh pieces of cornea (or other tissue to be ope-   and
rated on) are put into solution of chloride of gold of 0.5 per
cent. strength until they are thoroughly yellow, and then ex-
posed to the light in water acidulated with acetic acid until
the gold is thoroughly reduced, which happens in the course
of a few days at latest. They are then mounted in acidulated
glycerin.
The method in this, its primitive form, often gave splendid   vtht
results, but was very uncertain, giving sometimes a nuclear
or protoplasmic stain, sometimes an extra-cellular impregna-    &eAU
tion similar to that of nitrate of silver. And the preparations  oothr
thus obtained are not permanent, seldom keeping for more
than a few months.                                              leseth
Of late years very important improvements in the gold        Suieb
process have been worked out. In order to facilitate the        sit Clt
penetration of the gold and its subsequent reduction in the     P th
tissues, the tissues are made to swell up by treatment with       6 b(
formic acid before being brought into the gold bath, and         F, ed
formic acid is employed to assist the reduction after impreg-    dlIyl
nation. This is the principle of the process known as the       eiml
" method of L6wit."    Quite recently this method has been,      tiliui
as it seems to the author, improved in important respects by     vittol
'Virchow's Arch.,' Bd. xxxviii, pp. 346-349.  'Stricker's Handb.,'  ilid
p. 1100.                                                         td
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