These are solid and tenacious compounds, adhesive at the ordinary heat
of the human body; they owe their consistence to different causes, viz.
1. _To a due admixture of wax or fatty matter_, _and resin_, e. g.
_Emplast: Ceræ_, &c.
They may be said to differ only in _consistence_ from liniments,
ointments, and cerates; Deyeux[312] accordingly proposes to distinguish
them by the appellation of _Solid Ointments_.
2. _To the chemical combination of the semivitreous oxide of lead with
oils or fat_, e. g. _Emplast: Plumbi_.
3. _To the chemical action of the component parts of the plaster on
each other_, as _Emplast: Ammoniaci_, &c.
Plasters are generally kept in rolls, wrapped in paper, and when to be
used they are melted and spread on leather; in performing this operation
the practitioner ought not to apply a heat above that of boiling water;
for if metallic oxides be present, the fatty matter will, at a higher
temperature, reduce them, in consequence of the powerful affinity of oil
for oxygen at an exalted temperature; and if aromatic substances enter
as ingredients they will thus suffer in their strength, besides which
the fat itself will undergo a very injurious change by a mismanaged
application of heat, and the plaster will be less adhesive.
They are employed as remedies to answer two general indications;
_mechanically_, to afford support to muscular parts and to prevent the
access of air; and _medicinally_, to operate as stimulants, discutients,
rubefacients, or anodyne applications. That by affording an artificial
support to the various parts of the body, by the application of
plasters, we are capable in certain diseases of effecting much benefit,
is a truth to be explained upon the principles of physiology, and is
daily confirmed by the results of practice; thus by giving support to
the muscles of the back, how frequently the stomach is steadied and
strengthened? Diseases of the kidneys are in the same way very
frequently relieved by tight bandages around the loins; the existence of
an intimate connexion between the external and internal parts is
strikingly exemplified by the distressing effects which are often
experienced in weak habits, such as sickness, giddiness, and other
uneasy sensations, from a want of any usual compression, as that of
stays, under-waistcoats, &c. The support afforded to persons who have
been tapped in Ascites is another instance. I have also lately met with
a case in which a morbidly relaxed state of the bowels had harassed the
patient for several years, and set at defiance every astringent
medicine; upon the application, however, of a tight bandage around the
abdomen, the healthy action of the intestines has been completely
restored. Sir Gilbert Blane has suggested the trial of mechanical
compression of the head in the cure of Hydrocephalus, and several cases,
apparently favourable, have been published. Dr. Thackrey of Cambridge
has related a very interesting history in support of the practice, and
judiciously recommends the substitution of straps of adhesive plaster
for the bandages of cloth originally proposed by Sir Gilbert. In
reasoning upon this treatment, it will be found strictly conformable
with the soundest principles of physiology, and with those views in
particular, for the illustration of which I have here directed the
reader’s attention to the subject. Where our object is simple support,
we should of course select a plaster which is the most adhesive and the
least irritating. Many plasters which have gained great celebrity for
their curative virtues will be found to owe all their powers to their
adhesiveness, such is the _Emplastrum Oxidi Ferri Rubri_ of the
Edinburgh Pharmacopœia, for it is impossible that the iron should
communicate any tonic effect. The same observation applies to many of
those empirical plasters which have at different times acquired so great
a share[313] of popular applause. In the cure of sore legs[314] the
importance of adhesive strapping is generally acknowledged, and on such
occasions nothing is superior to the _Emplastrum Resinæ_.