102 
Transactions of the 
rMonthly Microscopical 
L Journal, Feb. 1, 1869. 
The whole section can rarely or ever be prepared in a perfectly uni- 
form manner, certain parts of it may be most admirable, whilst 
others may be either too transparent or too opaque. Whilst this 
mars the beauty of the preparation, it presents certain advantages 
occasionally, and may assist us to work out the histological details 
of a tissue. By the aid of this method, I have been able to make 
some important observations upon the minute anatomy of the 
cerebellum more especially, which will, I hope, soon be published. 
On Tinting with Chloride of Gold and other Metallic Prepa- 
rations. — Many people seem to experience some difficulty in the 
use of chloride of gold as a tinting agent, on account of the un- 
certainty of its action and the irregularity with which it stains the 
tissue. Dr. Beale speaks somewhat shghtingly of it on that 
account, and I at first experienced the same difficulties when 
attempting to use it in the manner recommended by Gerlach. I 
found that sometimes the gold did not stain the tissues at all, but 
was reduced for the most part in a molecular condition in and upon 
them, whilst at other times the tissue was tinted, but in a most 
unequal and irregular manner. I have for some time past, however, 
succeeded in overcoming all these difficulties by the use of a different 
reducing agent, and can now recommend the following method as 
one which will yield constant and satisfactory results ; the colour 
obtained being generally a rich purple, which undergoes no change 
whatever. The sections or portions of tissue are to be placed in 
a solution of chloride of gold (about 1:2000) made with water 
acidulated by hydrochloric acid in the proportion of one drop of the 
strong acid to two-and-a-half ounces. The sections are allowed to 
remain in this solution, protected from the hght for one hour, are 
then removed, and moved about for a few seconds in acidulated 
water only half as strong as that mentioned above, and then trans- 
ferred to a watch-glass or small capsule containing equal parts of 
formic acid * and of spirits of wine. This acts as a reducing agent 
and does not seem to injure the tissue in the least. The length of 
time required for reduction varies altogether with the temperature 
of the solution ; if this be made lukewarm by placing the capsule 
near a fire, the reduction and staining of the tissue may be complete 
in about half-an-hour, whilst if the solution be kept cold, the same 
amount of reduction may not be brought about in less than three 
or four hours. The solution must never be placed too near the 
fire, however, since the formic acid and spirit, when hot, will 
damage the specimen as much as if it had been placed in pretty 
strong acetic acid. 
If it be desired to tint very rajpidly as well as permanently, 
* I tried many reducing agents, but found formic acid by far the best. What 
I have employed has been analyzed and found to contain about nine or ten per cent, 
of the pure acid (0 O2). 
