medicinally.

CAROLINE.

Is it from this substance that castor oil is obtained?

MRS. B.

No. Far from it, for castor oil is a vegetable oil, expressed from the
seeds of a particular plant; and has not the least resemblance to the
medicinal substance obtained from the castor.

_Silk_ is a peculiar secretion of the silk-worm, with which it builds
its nest or cocoon. This insect was originally brought to Europe from
China. Silk, in its chemical nature, is very similar to the hair and
wool of animals; whilst in the insect it is a fluid, which is
coagulated, apparently by uniting with oxygen, as soon as it comes in
contact with the air. The moth of the silk-worm ejects a liquor which
appears to contain a particular acid, called _bombic_, the properties of
which are but very little known.

EMILY.

Before we conclude the subject of the animal economy, shall we not learn
by what steps dead animals return to their elementary state?

MRS. B.

Animal matter, although the most complicated of all natural substances,
returns to its elementary state by one single spontaneous process, the
_putrid fermentation_. By this, the albumen, fibrine, &c. are slowly
reduced to the state of oxygen, hydrogen, nitrogen, and carbon; and thus
the circle of changes through which these principles have passed is
finally completed. They first quitted their elementary form, or their
combination with unorganised matter, to enter into the vegetable system.
Hence they were transmitted to the animal kingdom; and from this they
return, again to their primitive simplicity, soon to re-enter the sphere
of organised existence.

When all the circumstances necessary to produce fermentation do not take
place, animal, like vegetable matter, is liable to a partial or
imperfect decomposition, which converts it into a combustible substance
very like spermaceti. I dare say that Caroline, who is so fond of
analogies, will consider this as a kind of animal bitumen.

CAROLINE.

And why should I not, since the processes which produce these substances
are so similar?

MRS. B.

There is, however, one considerable difference; the state of bitumen
seems permanent, whilst that of animal substances, thus imperfectly
decomposed, is only transient; and unless precautions be taken to
preserve them in that state, a total dissolution infallibly ensues. This
circumstance, of the occasional conversion of animal matter into a kind
of spermaceti, is of late discovery.