THE PRESERVATION OF MARINE ANIMALS. 119
large quantities at a moderate cost in the form of methylated spirit,
which is ethyl alcohol adulterated with methyl alcohol or wood spirit,
and other impurities. The adulteration usually causes no difficulties
to the zoologist, but it is essential that the methylated spirit should
be capable of mixing with water in any proportion without producing
any turbidity or any precipitate.
Modern improvements and refinements in the preservation of
marine animals consist in the preliminary treatment of the specimens
before they are finally placed in alcohol. The application of alcohol
offers difficulties of two distinct kinds. In the first place there are
physical difficulties depending on the difference of density between
alcohol and water, and the absorption of water by alcohol. These
difficulties present themselves in applying alcohol to a dead but
otherwise fresh specimen in good condition. Alcohol coagulates the
tissues and substance of which the specimen is composed, hardens
them, and preserves them from putrefaction or any further change of
any kind. But while it hardens thems it rapidly abstracts the water
from them, and thus causes soft tissues to contract and shrink until
the original shape and appearance of the specimen is entirely lost.
To a great extent, or even in some cases entirely, these difficulties
may be surmounted by adding the alcohol to the water which con-
tains the specimen very gradually, or by the simpler method of
placing the specimen successively in mixtures of water and alcohol in
different proportions, beginning for instance with a mixture containing
ten per cent. alcohol, and ending with one containing seventy or
ninety per cent.
The other difficulties present themselves in dealing with living
specimens. The original and primitive method was to plunge the
living specimen into "strong spirit," so as to kill it and preserve it
at the same time. The consequence of this is that in addition to the
distortion and shrinking caused physically by the abstraction of water
from the tissues, there occurs a still more violent contraction of all
the muscles of the creature, produced by the irritating action of the
alcohol on the sensory nerves. A great many of the lower marine
animals are endowed with some contracting mechanism particularly
adapted to the purpose of withdrawing the more delicate and
important organs either into a hard protecting structure, such as a tube
or shell, or into the interior of the rest of the body. Such animals
are often extremely sensitive, and at the least irritation their beautiful
and interesting organs disappear from view, remaining concealed