Medicines which are capable of shielding sensible surfaces from the
action of acrid matter, by involving it in a mild and viscid medium.
It cannot be denied that where these remedies admit of direct
application, considerable benefit may arise; in the progress of a
catarrh, we have all experienced the relief that may be occasioned by
lubricating the fauces with demulcents, which, by soothing the top of
the trachea, quiets, by a kind of contiguous sympathy, the whole
pulmonary structure; in certain states of intestinal irritation, the
same remedies have furnished considerable benefit, and in ophthalmia,
relief has been obtained by the application of a demulcent to the
inflamed conjunctiva, by which it is defended from the irritation of the
tears; see also _Formula 61_; but in parts beyond the reach of the first
passages, and to which no fluid can arrive but through the medium of the
secretions, it is very difficult to explain the principle upon which
their beneficial operation can depend; and it seems indeed highly
probable that they act in such cases as simple diluents, for the process
of digestion must necessarily deprive them of their characteristic
viscidity. The administration of demulcent drinks in gonorrhæa is
probably of no farther service in assuaging the _ardor urinæ_, than an
equivalent quantity of pure water; although Dr. Murray observes, “it is
sufficiently certain, that many substances, which undergo the process of
digestion, are afterwards separated in their entire state from the
blood, by particular secreting organs; and there is, continues he, no
gland which has this power more particularly than the kidneys;
substances received into the stomach and digested, afterwards passing
off in the urine with all their peculiar properties.” This is
undoubtedly very true, but mucilaginous substances rarely or never pass
off in this manner; if they evade the assimilative functions, they pass
through the alimentary canal, and are thus eliminated. I can state, as
the result of experiment, that the urine undergoes no change except in
the relative proportion of its water, by the copious and repeated
administration of mild mucilages. Dr. Saunders has very justly remarked
that the long list of _Ptisans_, _Decoctions_, _&c._ usually prescribed
upon these occasions, generally owe their virtues to the watery diluent
itself.
The pharmaceutical applications of this class of medicines constitute,
perhaps, not the least part of their value, by which we are enabled to
introduce acrid substances into the stomach with safety and effect; but
such services will more properly fall under our notice in a future part
of the work.