58 
transferred to distilled water, acidified with acetic acid, so as 
to be just acid to the taste. It is better to prepare several 
strips at once, and give them various amounts of exposure to 
the gold solution. The vessel containing the acidified water 
should be placed in the strongest light possible for about 
twenty-four hours, or till the tissue has become of a purple 
colour, and the nerve plexus distinctly visible to the naked 
eye. Glycerine should be used for mounting. 
Cornea.—The cornea of frogs and animals up to the size 
of a rabbit may be cut out whole, and so treated with the 
gold solution. Larger cornez, such as those of the ox, it is 
better first to render more permeable to the reagent by 
cutting them into thick sections parallel to the surface. The 
cornea should remain in the solution till it assumes a pale 
straw colour, and should then be treated in the same manner 
as Auerbach’s plexus. The frog’s cornea can be mounted 
whole, but from the thickest mammalian cornez sections 
must be cut with a razor. 
Before mounting the frog’s cornee, the epithelium of the 
conjunctiva and of Descemet’s membrane should be scraped 
off as clean as possible. In mammalian cornee, if it be 
wished to show the finest nerves among the epithelium, the 
corneze may be imbedded in pith, or a mixture consisting of 
about half white wax, and half olive oil, and vertical sections 
made of it. Or the epithelium may be partly removed and 
partly left an stfu, and a thin section made parallel to the 
surface, so as to be viewed from above. 
The results of gold preparation of the cornea are very 
uncertain ; sometimes the nerves only are stained, sometimes 
the connective-tissue-corpuscles ; sometimes, again, though 
the cornez assumes a beautiful purple colour, neither of these 
structures are to be seen at all. Again, a remarkable fact, 
the two cornee from the same frog may be removed at the 
same time, and treated together all through; and yet one 
may show the corpuscles, and scarcely any nerves; the other, 
all the nerves, and no corpuscles. At all events, the two 
always differ considerably. Whether this arises from some 
slight difference in the physiological state of the tissues of the 
two cornez, or perhaps from slight differences in the amount 
of light which they receive, though exposed together in the 
same vessel, it would be interesting, if possible, to determine. 
It is difficult to give any exact time for exposure to the 
action of the gold solution. A healthy frog’s cornea requires to 
remain in the solution about halfanhour. <A cornea that has 
been inflamed by means of a thread or caustic, with a view to 
Stricker’s observations on inflammation, requires only about 
