Chapter III: OF MEDICINES WHICH OPERATE mechanically

_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.

SIALOGOGUES;

Substances which increase the salivary[166] discharge. This class comprehends two orders of medicines, viz.

1st. Those which increase the salivary excretion by _external_ application to the secreting vessels, by mastication, as the following acrimonious and pungent substances, _Anthemis Pyrethrum_; _Colchearia Armoracia_; _Daphne Mezereum_; _Nicotiana Tabacum_, &c.

2nd. Those whose _internal_ exhibition affects these organs through the medium of the circulation, of which _Mercury_ is the only true example; for all the preparations of this metal, when administered in certain quantities, produce salivation.

The acrid Sialogogues, or Masticatories, by stimulating the excretory ducts, and increasing the secretion of saliva, sometimes relieve the pain of tooth-ache, and are commonly resorted to for that purpose; they are besides supposed capable of relieving other congestions, or inflammatory dispositions, in remote parts of the head, by the derivation they occasion from the neighbouring vessels, especially the branches of the external carotid.

Mercury, in its metallic state,[167] is perfectly inert, and does not exert any influence whatever upon the living body: this fact is sufficient, if any serious refutation were necessary, to overturn the theory which attributes its sialogogue property to the gravity of its particles, by which “it is disposed to retain the _direct line_ in which it is propelled from the heart, and is therefore more certainly determined to the vessels of the head.” It has been also supposed to act by diminishing the _lentor_ of the blood, and disposing it to pass more easily into the salivary glands, so as to increase their secretion: equally gratuitous and improbable are the chemical hypothesis which have been offered to explain this curious and singular property; Dr. Cullen endeavoured to solve the problem, by supposing that “_Mercury has a particular disposition to unite with ammoniacal salts, and that such salts are disposed to pass off by the salivary glands more copiously than by any other excretion_.” Dr. Murray, however, very justly remarks that mercury has not any peculiar tendency of this kind; and that if it had, these salts are not more abundant in the saliva, than in some other secretions. Dr. Murray then proceeds to submit a theory which he considers better calculated to explain the phenomenon; he observes, that the urine appears more peculiarly designed to convey matter which has been received into the circulating mass, but which is still excrementitious, from the system. To pass, however, with this fluid, it is necessary that the matter conveyed should be soluble in it; and when it is so, we can discover it in the secretion by chemical tests. If there is any property connected with it, therefore, which shall prevent this solubility, it probably will prevent the substance from being secreted. Now, the _phosphoric acid_, abundant in urine, must in this mode counteract the secretion of mercury in any form of preparation, by forming with it a compound, insoluble, and to which the slight excess of acid cannot communicate solubility; the mercury, therefore, existing in the circulating mass, when brought in the course of the circulation to the secreting vessels of the kidneys, will not pass through their whole course; but if conveyed so far as to be combined with _phosphoric acid_, will, from this combination, be incapable of being conveyed onwards, and will therefore be retained in the composition of that part of the blood which does not enter into the secretion, but returns into the circulation. It must be discharged by some other emunctory; a portion of it appears, from some facts, to pass off by the insensible perspiration; but the _tenuity_ of this secretion, if the term may be employed, must be unfavourable to this mode of discharge. The salivary secretion is one by which it may be more easily transmitted; and this transmission may even be facilitated by the affinity exerted to the _Oxide of Mercury_ by the _Muriatic Acid_, the _Soda_, and _Ammonia_, which are the chief saline ingredients in saliva; for it deserves to be remarked that triple compounds of these substances are, to a certain extent, soluble in water; and if the _Mercury_ is thus secreted, it will of course stimulate the secreting vessels through which it passes, and increase the discharge.

Sir Gilbert Blane[168] has lately advanced another hypothesis to account for the effects of mercury as a sialogogue; he considers the salivary glands as one of the outlets for the _ramenta_ of the bones, for by analysing the saliva we discover the principles of which they consist; indeed the osseous matter not unfrequently concretes on the teeth, and sometimes on the salivary ducts, in the form of what is called _Tartar:_ “does not this fact,” says Sir Gilbert Blane, “in some measure account for these glands being the parts upon which determination is made by the operation of mercury, which consists in exciting an active absorption of solid parts, as I have elsewhere observed?”[169]

But do not the kidneys, and other excretory glands also furnish outlets, through which the _detritus_ of the body is eliminated. How does it happen, therefore, that the kidneys are not as equally affected as the salivary glands by the action of mercury? In the present state of our knowledge it will be more prudent to rest on the phenomenon as an ultimate fact, than in attempting to ascend higher in the scale of causes, to involve ourselves in impenetrable darkness.

During the prevalence of the theory which attributed to _Nitric acid_ all the antisyphilitic powers of mercury, it was even maintained that this acid also excited ptyalism; experience however has disproved the effects thus attributed to it, and no one attempts to support its pretensions, as a sialogogue, except indeed as it may perchance, by its acrid qualities, influence the excretory ducts of the glands, externally, in the act of being swallowed.

It has very lately been stated by Dr. Macleod,[170] that the _Hydro-cyanic acid_ occasionally produces soreness of the gums, and a disposition to ptyalism; this, if true, is a very remarkable fact, and well deserves attentive consideration.

Some theorists may, perhaps, be inclined to consider certain Nauseating Medicines as possessing sialogogue properties. It cannot be denied that an increased discharge of saliva will take place during the operation of such remedies, but it is very transient, and can never be rendered available to any therapeutic object. I shall however have occasion to refer to this fact hereafter, and to the inference deduced from it by Dr. Eberle, in explanation of the effect of nauseating medicines in promoting the operation of Mercury.

ERRHINES, or STERNUTATORIES:

Substances which, by direct application to the pituitary membrane, occasion a discharge from the nostrils either of a mucous or serous fluid. This class contains several different species, whose operation varies in intensity, as well as in duration.

Errhines have been regarded as useful in consequence of the evacuation they occasion, but in this respect their value has been greatly over-rated; it has been stated, that they diminish the quantity of fluid circulating in the neighbouring vessels, and even extend their influence to all the branches of the external carotid; and Dr. Cullen says that he has, apparently from this operation, known head-ache, pain of the ear, and some cases of ophthalmia, cured or relieved by the use of Errhines. There can be no doubt that local stimulants of this kind will frequently remove pain from the head and neighbouring parts, but not merely by occasioning vascular depletion, as Dr. Cullen supposed, but by a stimulant operation conveyed through the medium of nervous communication, or contiguous sympathy.

Dr. Cullen has moreover supposed, that these substances may be useful in preventing apoplexy or palsy. Morgagni[171] however relates a case in which sneezing induced a fatal attack of this disease; and Van Swieten[172] has satisfactorily shewn, that continued paroxysms of sneezing tend to load the vessels of the head with blood; for the violent contraction of the chest impedes, for a time, the passage of the blood through the lungs, and therefore obstructs the return of the venous blood from the brain, the vessels of which are in consequence greatly distended; the face therefore reddens and becomes turgid, the eyes are suffused with water, and appear full and distended. Its occasional dangerous violence is said to have given origin to the benediction so universally bestowed on those who sneeze.[173]

It has been a subject of popular inquiry, how far the habitual use of Snuff may prove beneficial or injurious; and whether the habit, when once fully established, can be discontinued with impunity? It may be remarked that Snuff, by habitual use, soon ceases to produce the effect of an Errhine, for which reason its discontinuance cannot, generally, be regarded as likely to be attended with any danger; in those cases, however, in which the discharge is perpetuated, a contrary judgment should be pronounced, for all artificial discharges become constitutional by long continuance, and can therefore be seldom checked with impunity. Dr. Cullen states, from experience, that “whenever the nasal discharge has been considerable, the laying aside the custom of taking snuff has been productive of evil.”

EPISPASTICS. _Vesicatories._ _Blisters._

External applications to the skin, which produce a serous or puriform discharge, by previously exciting a high state of inflammation.

When these agents act so mildly as merely to excite inflammation, without occasioning the effusion of serum, they are denominated RUBEFACIENTS.

Various substances have at different times, been proposed for the accomplishment of this object,—such as _Nitric Acid_, _Boiling Water_, _Strong Acetic Acid_, _Tartarized Antimony_, &c. It is, however, generally admitted, that no substance ever employed equals in efficacy, or certainty, the _Cantharis Vesicatoria_, the common blistering, or Spanish fly; and whose effects may serve to illustrate the _modus operandi_ of this class of remedies.

By the application of a _Blister_, the extreme blood vessels are excited into increased action, by which inflammation is occasioned, and the exhalants made to pour out a thin serous fluid which separates the cuticle from the true skin, and forms a vesicle or blister.

From this simple view of the subject it will appear evident, that blisters may produce their salutary effects by several different modes of operation; by a just estimate of which the practitioner will be enabled to reconcile the discordant opinions which have been delivered upon the subject, and to employ these agents with greater satisfaction and advantage.

Blisters may act—

1. AS DERIVATIVES, i. e. _by producing a derivation of the circulation
from the inflamed and engorged vessels of the neighbouring organs
to the blistered surface_. This mode of operation was long
overlooked by the physicians, who ascribed all the beneficial
effects of a blister to the evacuation which it produced, while
the humoral pathologist, moreover, considered the matter so
discharged to be of a morbific nature. That such agents owe their
salutary tendency to causes independent of their powers as
evacuants, is at once rendered evident by the relief which they
afford, when used only as Rubefacients.

2. AS EVACUANTS—_by occasioning an effusion of Fluids_. In this case
the vesicated part may be considered in the light of a new
excretory organ, the formation of which requires the establishment
of a new current or determination of blood; so long as the
discharge continues, so long will there be an especial demand of
blood in the blistered part, and a consequent derivation of the
circulation from the inflamed and engorged vessels of the
neighbouring organs.[174] The nature of the fluid effused is at
first serous, but after some time it becomes purulent, and this
stage of its operation must be considered as, by far, the most
beneficial; hence the great advantages derived from a “_perpetual
blister_.”

3. AS GENERAL STIMULANTS, _by raising the vigour of the
circulation_.[175] That Blisters have such a tendency there exist
too many proofs to allow us to doubt. Hence in fevers they
frequently prove valuable auxiliaries, but since the application
of any stimulus, in such diseases, must be regulated by the degree
of excitement, it is evident that they can only be made with
success in particular stages; this simple fact will at once
explain the cause of that want of unanimity in Physicians with
respect to the value of blisters in febrile diseases. Rush
considered that there was one particular period, in the course of
a continued fever, intermediate between its stage of high
excitement and the appearance of a collapse, in which blisters
will generally produce unequivocal good effects, and to this he
gave the name of the _Blistering point_.

4. AS ANTISPASMODICS.—_Relieving pain through the medium of Contiguous
Sympathy._ This effect would frequently appear to be independent
of the operations above enumerated; a similar principle seems to
exist with regard to the _pain_ excited by blisters, which may
also be applied to the explanation of the advantages derived from
them in several diseases. It has long been remarked that, by
exciting one pain we may often relieve another, and hence blisters
afford relief in tooth-ache, and other painful affections.
Epilepsy and Hysteria, arising from irritation, have been removed
by such applications, apparently from their exciting powers.

It remains for us to make a few observations upon the abuse of these remedies, for, notwithstanding the popular adage that “_Blisters are always safe things_,” that “_if they do no good, they can do no harm_,” they will be found, like all other potent applications, capable of producing much mischief when directed by unskilful hands. In stages of high vascular excitement in the pulmonary organs, blisters have increased the irritation they were designed to allay, and in some cases have promoted a tendency to effusion; in the treatment of acute Hydrocephalus the common practice of blistering the head appears very questionable, and has too often, I am well persuaded, accelerated the fatal termination, by increasing the disposition to serous effusion.

ISSUES (_Fonticuli_) and SETONS (_Setacea_[176]).

The effects of these processes bear a strong analogy to those which are produced by Vesicatories; they are, however, more permanent, and are on that account better adapted to the relief of those chronic affections which would seem to require a remedy of long continued influence. In pulmonary affections, for instance, a seton in the side is frequently attended with very considerable benefit. The popular belief in humoral pathology, which continues to influence the mass of mankind, has perhaps assigned to these remedies a greater share of credit than that to which they are really entitled, but it must still be acknowledged that when an ulcer having existed a great length of time, is healed or _dried up_, or any constitutional discharge is suddenly checked, the health may become affected. In such cases the establishing a discharge by means of an Issue is undoubtedly a safe, and often a beneficial operation.