Medicines which quicken or increase the evacuation from the intestines,
or which, when given in a certain dose, occasion purging.
These remedies, from a general difference in their modes of operation,
have been classed under two divisions—LAXATIVES and PURGATIVES. The
former operate so mildly that they merely evacuate the contents of the
intestines, without occasioning any general excitement in the body, or
even stimulating the exhalant vessels of the canal; the latter produce a
considerable influx of fluids from these vessels, and extend their
stimulant effect to the system in general; and where these effects are
very violent, the purgative is further distinguished by the epithet
DRASTIC. Laxatives then may be said to empty the bowels simply, and to
carry off extraneous matter, which is out of the course of the
circulation; but purgatives, as they occasion a constitutional effect,
may be made subservient to very important purposes. The effects of a
purgative may depend upon three different modes of operation; viz.
1. _By stimulating the muscular fibres of the Intestines, whence
their peristaltic motion is augmented, and the contents of the
bowels more quickly and completely discharged._
2. _By stimulating the exhalent vessels, terminating in the inner
coat of the intestines, and the mouths of the excretory ducts of
the mucous glands; by which an increased flow of serous fluids
takes place from the former, and a more copious discharge of
mucus from the latter; the effect of which is to render the fæcal
matter thinner and more abundant._
3. _By stimulating the neighbouring viscera, as the Liver and
Pancreas, so as to produce a more copious flow of their
secretions into the intestines._
It appears that different purgatives have very different powers in
relation to the several modes of operation above specified; some
medicines, for example, urge the bowels to evacuate their contents by an
imperceptible action upon the muscular fibres, and little or no increase
of serous discharge attends the evacuation, such are _Manna_, _Sulphur_,
and _Magnesia_; there would seem, moreover, to be certain bodies that
have the property of increasing the peristaltic motions by operating as
mechanical stimulants upon the fibre; it would not be difficult to
derive many illustrations of this fact, from the history of herbivorous
quadrupeds, and I have been disposed to consider the harsh and coarse
texture which certain grasses assume in moist situations, as a wise
provision in Nature to furnish an increased stimulus to the intestines
of the animals who feed upon them, at a time when their diminished
nutritive qualities must render such a result desirable; but the
operation of a mechanical laxative may be demonstrated by a more
familiar example; the addition of bran to our bread, constituting what
is known by the name of _Brown bread_, induces laxative effects, merely
from the mechanical friction of the rough particles, or scales of the
bran, upon the inner coats of the intestines, for the wheat without the
bran in bread is not particularly laxative.[154] Other cathartics
stimulate the fibres to a much greater degree, and the effects are
either confined to a part of the canal, or communicated to the whole
range of the intestines, from the duodenum to the extremity of the
rectum; _Aloes_ will furnish a good example of the former, and
_Colocynth_ may be adduced as an instance of the latter mode of
operation. Other cathartics, again, direct all their stimulus to the
exhalant vessels, and are accordingly distinguished by the force with
which they produce serous evacuations; and for which they were formerly
denominated _Hydragogues_, such are _Saline Purgatives_, and certain
vegetable bodies to be hereafter described. Dr. Cullen has even supposed
that some of these medicines may act solely in this way, and without
increasing directly the peristaltic motion; there is, however, as Dr.
Murray very justly remarks, no proof of such an hypothesis, and it seems
scarcely probable that any substance should act as a stimulant on these
vessels, without at the same time stimulating the mobile fibres of the
intestines. _Mercurial Purgatives_ appear to possess, in an eminent
degree, the power of exciting the functions of the liver, and of thereby
occasioning an influx of bile into the intestines. From the indications
which cathartics are capable of fulfilling, their utility in many
diseases must be apparent; the extent of their importance and value
were, however, never justly appreciated until the valuable publication
of Dr. Hamilton on this subject, in which the author has pointed out
with more precision than any preceding writers had done, the therapeutic
principles which should regulate their administration. His practice has
clearly proved that a state of bowels may exist in many diseases, giving
rise to a retention of feculent matter, which will not be obviated by
the occasional administration of a purgative, but which requires a
continuation of the alvine stimulant, until the healthy action of the
bowels is re-established. Since this view of the subject has been
adopted, numerous diseases have received alleviation from the use of
purgatives that were formerly treated with a different class of
remedies, and which were not supposed to have any connection with the
state of the alvine evacuations; thus in fever, the peristaltic motion
of the intestines is diminished, and their feculent contents are unduly
retained, and perhaps, in part, absorbed, becoming of course a source of
morbid irritation; this fact has long been understood, and the practice
of administering cathartic medicines under such circumstances has been
very generally adopted; but until the publication of Dr. Hamilton,
physicians were not aware of the necessity of carrying the plan to an
extent beyond that of merely emptying the _primæ viæ_, and they did not
continue the free use of these remedies through the whole progress of
the disease.
Cathartics are essentially serviceable also in several diseases of the
class NEUROSES, which are generally intimately connected with a morbid
condition of the alimentary passages; _Chorea_ and _Hysteria_ have been
very successfully treated in this manner. The diseases incident to
puberty in both sexes are also best relieved by a course of purgative
medicines, and their effects in _Chlorosis_ have conferred upon many of
them the specific title of EMMENAGOGUES.
But the therapeutical utility of Cathartics extends beyond the mere
feculent evacuations which they may occasion. In consequence of the
stimulating action which some of them exert upon the exhalent vessels,
they abstract a considerable portion of fluid from the general current
of the circulation, and are, on that account, beneficial as
_Anti-phlogistics_. For the same reason they may act as powerful
promoters of absorption, for there exists an established relation
between the powers of exhalation and absorption, so that when the action
of one is increased, that of the other is augmented.
Certain Purgatives, as I have just stated, exert their influence upon
the neighbouring organs, and are calculated not only to remove alvine
_sordes_, but to detach and eliminate foul congestions from the biliary
ducts and pores.
With such facts before us, it is impossible to concede to the opinion of
Dr. Hamilton,[155] that the different species of purgative medicines _do
not possess distinct powers over the different species of matter to be
evacuated_; on the contrary, there is reason for reviving the ancient
theory, too inconsiderately abandoned, and which acknowledged these
different distinctions in the operations of cathartic medicines, under
the appropriate names of _Hydragogues_, _Cholagogues_, &c.
The importance of cathartic medicines having been shewn, and the
distinctions in their modes of operation established, it only remains to
say a few words upon the subject of their abuse. All the remedies of
this class, but more especially those of considerable power, require
caution in their administration, even in those diseases where they are
indicated by peculiar symptoms, especially if there be any tendency to
inflammation, or to extreme debility, although this latter symptom is
often rather apparent than real, and is at once removed by the brisk
operation upon the bowels; during pregnancy and immediately after
delivery, and during the flow of the menses, the prudent practitioner
will use a discretionary caution in their exhibition. The too frequent
use of these medicines will induce marasmus, and render the bowels so
morbidly irritable, that purging is easily excited by the ordinary
stimulus of our aliments; while in some habits the contrary obtains, and
the resource to which the valetudinarian flies for relief only increases
the torpor of the intestines, and confirms his costiveness.
The mode of adapting, combining, and administering Cathartics, will
present subjects for our future consideration.