_a._ _By imparting vigour to the respiratory muscles, engaged in the act
of expectorating._
It must be admitted that, to a certain extent, expectoration is a
voluntary operation, connected with the action of a variety of muscles,
which in a state of extreme debility are not easily excited into action:
every practitioner must have noticed this fact during the treatment of
the coughs of exhausted patients, and have witnessed the distress
necessarily arising from it; in this condition, the exhibition of a
stimulant may so far renew the exhausted excitability of these organs,
as to enable them to undergo the necessary exertions.
_b._ _By compressing the thoracic viscera, through the operation of an
emetic._
The beneficial results which frequently attend the concussion of an
emetic, in cases of mucous accumulations in the lungs, are too well
known and understood to require much elucidation: in the act of vomiting
the thoracic viscera are violently compressed, the neighbouring muscles
are also called into strong action, and both expiration and inspiration
are thus rendered more forcible, and the expulsion of mucus from the
cavity of the lungs necessarily accomplished.
The safety and expediency of such a resource must, however, in each
particular case be left to the discretion of the medical practitioner.
Besides the remedies above enumerated, there are some others which
afford relief in certain coughs, and have therefore in popular medicine,
been considered as _Expectorants_; but their operation, if they exert
any, is to be explained upon principles altogether different from that
of facilitating expectoration, and will more properly fall under the
head of _Demulcents_.
Atmospheric changes, in relation to moisture and dryness, deserve some
notice before we conclude the history of expectorant agents: the subject
teems with curious and important facts, and the advantages which the
asthmatic patient derives from such changes merit farther investigation.
That the lungs are constantly giving off aqueous vapour is made evident
by condensing the expired air on a cold surface of glass or metal; and
it is easy to imagine that when the atmosphere is saturated with
moisture, its power of conducting off this vapour will be proportionably
diminished, and that an accumulation of fluid may thus take place in the
lungs; on the other hand, we may suppose the air to be so dry as to have
an increased capacity for moisture, and to carry off the expired vapour
with preternatural avidity; in either of these cases, the excretions
from the lungs will be materially influenced, whether to the benefit or
disadvantage of the patient will depend, in each particular instance,
upon the nature of the disease under which he suffers. I have known a
person who could breathe with more freedom in the thick fogs of the
metropolis than in the pure air of a mountainous region, and it would
not be difficult to adduce many examples in illustration of a
diametrically opposite constitution of the pulmonary organs.
From the same cause we may frequently observe remarkable changes occur
in the character of a cough, at the breaking up of a frost; in some
cases the expectoration will be checked, and in others promoted by a
sudden change from a dry to a moist atmosphere. Can a more instructive
illustration be offered of that important fact, which I have been
labouring in every page to impress upon the mind of the young
practitioner, that, _remedies are only relative agents_?
In the course of considerable experience in the treatment of pulmonary
complaints, and in the influence of climate and seasons upon them, I
have repeatedly observed the rapid transition from moisture to dryness
to occasion very remarkable effects upon the disease; and I much
question whether an attention to such a condition of the atmosphere does
not deserve as much consideration in the election of a suitable place of
residence for such invalids, as the more obvious circumstance of
temperature. I have been long in the habit of recommending to persons
confined in artificially warmed apartments, to evaporate a certain
portion of water, whenever the external air has become excessively dry
by the prevalence of the north-east winds, which so frequently infest
this island during the months of Spring; and the most marked advantage
has attended the practice. But in such cases the practitioner must ever
be guided by the symptoms of each particular case; it would be worse
than useless to lay down any general precept for his guidance. We cannot
then be surprised that such a difference of opinion should exist amongst
practitioners of equal eminence, respecting the influence of a marine
atmosphere; some advocating its advantages to the pulmonary invalid, and
others maintaining with equal confidence the injurious tendency of such
localities; each party appeals to _experience_ in justification of his
opinion, and with equal candour and justice; but the cases from the
results of which the medical inference has been drawn, however parallel
they may have appeared, differed in those essential points to which we
have alluded, and upon which the question of climate would seem to turn.
There is another circumstance connected with the subject of atmospheric
moisture which it is also essential to remember,—that the air gains a
considerable increase in its power of conducting caloric, by becoming
saturated with aqueous vapour; thus, when a thaw takes place, and the
thermometer rises a few degrees above 32°, the air, instead of
impressing us with the sensation of increased temperature, actually
appears much colder.