120 PROCEEDINGS OF SOCIETIES. 
tered in their optical characters for a period of two years : 
beyond this my experience does not extend. I imdeed have 
no reason for supposing that specimens which have remained 
so long unchanged should not continue well preserved ; fur- 
ther experience will, however, afford the surest means of 
determining the sufficiency of the medium as a preservative. 
Some recent and moist structures, animal and vegetable, 
admit of bemg mounted in Canada balsam without being 
previously dried ; the advantage of this is, that the parts of 
an object are not distorted, as must, to a greater or less ex- 
tent, always happen when a specimen is completely desic 
cated. The manner of proceeding is as follows: Take the 
specimen from the water or other liquid in which it has been 
prepared, let it drain a little, and then immerse it in rectified 
spirits of wine; after a short time (varying from one or two 
to ten or fifteen minutes, according to the size and thickness 
of the specimen), remove it from the alcohol, and, after 
draining, place it in methylic alcohol, otherwise known as 
pyroxilic spirit, pyro-acetic spirit, &c. After allowing it to 
remain a few minutes in this liquid, it may be removed, 
drained, and immersed in spirits of turpentine, on being 
taken from which, after a few minutes, it may be placed in 
balsam, and be proceeded with in the usual manner; the 
balsam ought to be sufficiently fluid not to need the employ- 
ment of heat. It is recommended to pass the specimen 
from common to methylic alcohol, and thence to spirits of 
turpentine, because the turpentine mixes more readily with 
the latter than with the former; observe, however, that 
the spirit referred to is TRuE methylic alcohol, or pyroxilic 
spirit, not what is commonly known as methylated spirit, which 
is common alcohol contaminated with wood-naphtha, &c. 
Injected preparations are well preserved and displayed in 
this way: there is no displacement or distortion of parts, and 
while the vessels are shown in their true position and rela- 
tions, the object is more securely and permanently preserved 
than if mounted in a cell with liquid in the ordinary manner ; 
for, notwithstanding the greatest care cells will leak, and 
there are I believe few collections which after a lapse of four 
or five years will not contain cells into which air has passed, 
and from which a corresponding quantity of the original 
liquid has escaped. It has been said that this way of 
mounting objects in Canada balsam is neither original nor 
new, and in order that merit may be given where, it is 
said, merit is justly due, reference has been made to some 
beautiful preparations of the nerves, &c., by Dr. Andrew 
Clark, put up in this way a year and a half or two years ago. 
