Chapter V: Preface (4)

CLIMATE also produces a powerful impression upon vegetable and animal life. It is probable that in southern countries some vegetables enjoy more energetic properties than in northern climes. The history of opium immediately countenances such an opinion; thus Egypt produces a stronger _opium_ than any of the countries on the north side of the Mediterranean,—France, than England or Germany;—and Languedoc, than the northern parts of France;—while Smyrna, Natolia, Aleppo, and Apulia, furnish a juice far more narcotic than Languedoc: so again, _Senna_ by transplantation from Arabia into the south of France (Provence) assumes a marked change in its physiognomy and virtues, its leaves are more obtuse, and its taste less bitter and nauseous than the pointed leaved variety, while its effects will be found to be less purgative. _Cruciform_ plants degenerate within the tropics, but acquire increased energies, as _Antiscorbutics_, in cold regions; the _Menthæ_ have not so penetrating an essential oil in the south of Europe as in England and in the north of France. The relative proportions of gluten vary in the wheat of different countries, and as in the south of Europe, its quantity greatly predominates over the other principles, we at once discover the cause that gives such excellence to the Maccaroni of Italy. Many species of plants secrete juices in warmer regions, which are unknown in their œconomy, in colder climates; thus the Ash yields _Manna_ in Calabria, but loses that faculty as it advances towards the north. The influence of climate, in its relations to moisture and dryness, upon vegetable productions, is also worthy of investigation; in wet and cold seasons, our herbage is far less nutritive to cattle, and we accordingly find that they are constantly grazing, in order to compensate by quantity, for what is deficient in quality, whereas in dry seasons, a larger proportion of their time is consumed in rumination; the same causes, however, that diminish the nutritive powers of plants, frequently increase the energy of those principles upon which their medicinal value depends: it is obvious that many herbs are more rank and virulent in wet and gloomy seasons: this would appear to be a wise and provident law, in order to apportion the natural condiment of the vegetable, to the deteriorated state of its nutritive elements, when the digestive organs must require more than the ordinary stimulus for the due exercise of their functions. It is hardly necessary to observe that plants, which in temperate climates are merely shrubs, have been developed into trees, by the hot and humid plains of Africa and Asia; while in the arid deserts of Nubia or in the frigid plains of Siberia, vegetable life is confined to stunted shrubs and humble mosses: cold also suppresses the colour of flowers, and indeed even that of the leaves, as is witnessed in the _Cyclamen_, _Amaranthus_, and _Ranunculus_ of Lapland and Siberia. But climate not only modifies the powers of a remedy by influencing its structure and composition, but it renders it more or less active, by increasing or diminishing the susceptibility of the body to its impression; can a more striking proof of this fact be adduced than the well known effects of perfumes at Rome? The inhabitants are unable to sustain the strong scent of flowers in that climate, without experiencing a sensation highly oppressive, and which in some cases is even succeeded by syncope,[119] and thus realising the well known line of the poet,

“_Die of a Rose, in aromatic pain._”

As I have been favoured with some very interesting observations upon this subject by Dr. Richard Harrison, who resided for a considerable time in Italy, and was thus enabled to institute a satisfactory inquiry into this curious subject, I feel no hesitation in introducing a quotation from his letter to my readers.—“You ask me what experience I have had on the subject of climate, as affecting the powers and operation of remedies; I have no difficulty in asserting that Narcotics act with greater force even in smaller doses at Naples, where I had the advantages of much experience, than in England. I might adduce as an example the _Extract of Hyoscyamus_, which, when given to the extent of three grains thrice a day, produced in two patients a temporary amaurosis, which disappeared and again recurred on the alternate suspension and administration of this medicine; and it deserves particular notice that these very patients had been in the habit of taking similar doses of the same remedy in England, without any unpleasant result. Now that this depended upon an increased susceptibility of the patient, in the warmer climate, rather than an increased power in the remedy, is unquestionable, since the extract which was administered in Italy had been procured from London; indeed a high state of nervous irritation is the prevalent disorder of Naples. I treated several cases of Epilepsy in Italy with the _nitrate of silver_, and with complete success, while in England I certainly have not met with the same successful results. During my residence at Naples, I spent some time in the island of Ischia, so celebrated all over the continent for its baths; many of the patients who were then trying their efficacy, had been attacked by Paralysis, Apoplexy, and almost every degree of loss of mental and muscular power, and among them I certainly witnessed what with propriety might be denominated a genuine case of _Nervous Apoplexy_. These complaints I was generally able to trace to the abuse of _Mercury_, whence we may, I think, very fairly conclude that this metal is more active in its effects in that, than in our own country. Before I quit this subject, I ought to mention that the doses of medicines, as seen in the prescriptions and works of English Physicians, excite universal astonishment among the faculty of Italy. In fact, as I have just stated, the human constitution in this part of the continent is certainly more susceptible of nervous impression than in England: it is perfectly true that flowers or perfumes in a chamber, will frequently produce syncope in persons apparently strong and healthy, and the fact is so universally admitted, that the Italians avoid them with the greatest caution.” On the other hand, it appears equally evident that some remedies succeed in cold climates which produce little or no benefit in warmer latitudes. Soon after the publication of the first edition of my Pharmacologia, I received a letter from Dr. Halliday of Moscow, upon the subject of the “_Eau Medicinale_,” and as it offers a striking proof of the efficacy of the _Rhododendron Chrysanthum_ in curing the rheumatism of the North, whilst in this country the plant has been repeatedly tried without any signal proof of success, I shall here subjoin an extract from the letter of my correspondent: “In reading your account of the ‘_Eau Medicinale_,’ I perceive that, upon the authority of Mr. James Moore, you state it to be a preparation of the _White Hellebore_; may I be allowed to suggest the probability of its being made from the leaves of the _Rhododendron Chrysanthum_? for so far as I can learn, the effects of the French medicine are precisely those which are experienced from an infusion of the above plant, which the Siberians and Russians regard as an infallible specific in the cure of chronic rheumatism and gout, and from which I myself, as well as other physicians in Russia, have witnessed the most desirable and decided effects, whenever we had it in our power to administer the remedy with confidence and courage. We have seldom given it in any other form or dose than that adopted by the Siberians themselves, which is to infuse in a warm place, generally near a furnace and during the night, two drachms of the fresh leaves in about twelve ounces of boiling water, taking care that the liquid never boils. This dose is to be taken in the morning upon an empty stomach, and during its nauseating operation, which generally commences within a quarter of an hour after it has been swallowed, neither solids nor liquids of any description are allowed; after an interval of three or four hours, I have seen the patient obtain a copious and black fœtid stool, and get up free from pain. Should it happen that the patient does not recover from the first dose, another is administered on the succeeding day, and I have known it to be taken for three days in succession, when the severest fits of gout have been removed.[120] Is it not then probable that some cunning Frenchman has availed himself of this Siberian specific, and concentrated it in such a form, as to defy all the learned to find it out?”

Dr. Halliday adds, “The Siberians denominate the leaves of this plant, when infused in water, _Intoxicating Tea_; and a weaker infusion is in daily use, especially for treating their neighbours, just as the Europeans do with tea from China.”

Before we quit the consideration of Climate, as being capable of influencing the activity of a remedy, the important fact should not be overlooked, that in India, and other colonies of similar temperature, Mercurial Medicines, in order to produce their beneficial effects, require to be administered to an extent which would prove destructive to the inhabitants of this island.

But of all the circumstances that produce the greatest change in the aspect as well as in the virtues of the vegetable creation, is CULTIVATION, which may either destroy the medicinal properties of a plant, or raise in it new and most valuable qualities: cultivation converts single into double flowers, by developing the stamens into petals, a change which in many cases destroys their efficacy, as in the camomile, _Anthemis Nobilis_; for, since all the virtues of this flower reside in the disc florets, it is of course greatly deteriorated by being converted into the double-flowered variety; by the operation of _grafting_ extraordinary changes may also be produced; Olivier, in his travels, informs us that a soft _Mastiche_, having all the qualities of that resin, except its consistence, which is that of turpentine, is procured by engrafting the Lentisk on the Chian Turpentine tree.

Buffon states that our wheat is a factitious production raised to its present condition by the art of agriculture. M. Virey[121] observes, that by suppressing the growth of one part of a plant we may respectively give rise to an increased developement in others; thus are some vegetables rendered eunuchs, or are deprived of seeds by obliteration, and only propagate themselves by slips; such a condition is frequently produced by culture, continued through a long succession of generations; this is the case with the _Banana_, _Sugar Cane_, and other fruits that have carefully been made to deviate for a long series of years from their original types, and having been continually transplanted by slips, suckers, or roots, at length only propagate themselves in this way, whereby the roots, as those of the common potatoe, become inordinately developed, drawing to themselves the succulence and nutrition originally possessed by the berries. It seems probable that we may thus have lost many vegetable species; the _Tuberes_ of Pliny, for example, are supposed by Mr. Andrew Knight to have been intermediate productions, formed during the advancement of the Almond to the Peach, or in other words that they were swollen almonds or imperfect peaches; if this conjecture be admitted, it will explain the fact stated by Columella, that the peach possessed deleterious qualities when it was first introduced from Persia into the Roman Empire. If there be any who feel sceptical upon the subject of such metamorphoses, let him visit the fairy bowers of Horticulture, and he will there perceive that her magic wand has not only converted the tough, coriaceous covering of the Almond into the soft and melting flesh of the Peach, but that by her spells, the sour Sloe has ripened into the delicious Plum, and the austere Crab of our woods into the Golden Pippin; that this again has been made to sport in endless variety, emulating in beauty of form and colour, in exuberance of fertility and in richness of flavour, the rarer productions of warmer regions, and more propitious climates! In our culinary vegetables the same progressive amelioration and advancement may be traced; thus has the acrid and disagreeable _Apium graveolens_ been changed into delicious _Celery_, and the common _Colewort_, by culture continued through many ages, appears under the improved and more useful forms of Cabbage, Savoy, and Cauliflower. It has been already observed that the alimentary and medicinal virtues are frequently in opposition to each other, and that while cultivation improves the former, it equally diminishes the latter; I shall have occasion to offer some additional facts upon this curious subject, under the consideration of _Bitter Extractive_; _see Note on this Extract, in the article_ “_Tonics_.”

THE IGNORANT PREPARATION AND FRAUDULENT ADULTERATION OF MEDICINES.

The circumstances comprehended under this head certainly deserve to be ranked amongst the more powerful causes, which have operated in affecting the reputation of many medicinal substances. The Peruvian Bark fell into total discredit in the year 1779, from its inability to cure the ague; and it was afterwards discovered to have been adulterated with bark of an inferior species; indeed Sydenham speaks of the adulteration of this substance before the year 1678; he tells us that he had never used to exceed two drachms of _Cinchona_ in the cure of any intermittent, but that of late the drug was so inert, rotten, and adulterated, it became necessary to increase its dose to one, two, or three ounces. The subject is copious and full of importance, and I have taken considerable pains to collect very fully, the various modes in which our remedies are thus deprived of their most valuable properties, and to suggest the best tests by which such frauds may be discovered. Very few practitioners have an idea of the alarming extent to which this nefarious practice is carried, or of the systematic manner in which it is conducted: there can be no doubt but that the sophistication of medicines has been practised in degree in all ages,[122] but the refinements of chemistry have enabled the manufacturers of the present day, not only to execute these frauds with greater address, but unfortunately, at the same time, to vend them with less chance of detection. It will be scarcely credited, when I affirm that many hundred persons are supported in this metropolis by the art of adulterating drugs, besides a number of women and children who find ample employment and excellent profit in _counterfeiting_ Cochineal with coloured dough, Isinglass with pieces of bladder and the dried skin of soles, and by filling up with powdered Sassafras the holes which are bored in spice and nutmegs, for the purpose of plundering their essential oils.

THE UNSEASONABLE COLLECTION OF VEGETABLE REMEDIES.

Vegetable physiology has demonstrated, that during the progress of vegetation most remarkable changes occur in succession, in the chemical composition, as well as in the sensible qualities of a plant; time will not allow me to be prodigal of examples, take therefore one which is familiar and striking,—the aromatic and spicy qualities of the unexpanded flowers of the _Caryophyllus Aromaticus_ (_Cloves_) are well known to every body, but if the flower-bud be fully developed it loses these properties altogether, and the fruit of the tree is not in the least degree aromatic; so the berries of Pimento, when they come to full maturity, lose their aromatic warmth and acquire a flavour very analogous to that of Juniper. The _Colchicum autumnale_ may be cited as another example in which the medicinal properties of the vegetable are entirely changed during the natural progress of its developement. See also _Inspissated Juices_, under the article _Extract_.

THE OBSCURITY WHICH HAS ATTENDED THE OPERATION OF COMPOUND MEDICINES.

It is evident that the fallacies to which our observations and experience are liable with respect to the efficacy of certain bodies, as remedies, must be necessarily multiplied when such bodies are exhibited in a state of complicated combination, since it must be always difficult, and often impossible, to ascertain to which ingredient the effects produced ought to be attributed.

How many frivolous substances have from this cause alone gained a share of credit, which belonged exclusively to the medicines with which they happened to be accidentally administered?[123] Numerous are the examples which I might adduce in proof of this assertion; the history of Bezoar[124] would in itself furnish a mass of striking evidence, indeed the reputation of this absurd substance was maintained much longer than it otherwise would have been, by its exhibition having been frequently accompanied with that of more active articles. Monardes, for instance, extols the efficacy of the _Bezoar_ as a vermifuge, but he states that it should be mixed with the seeds of _Wormwood_. Besides, in the exuberance of mixture, certain re-actions and important changes are mutually produced, by which the identity of the original ingredients is destroyed; but this subject will be introduced for discussion in the first part of the Pharmacologia.

The practice of mixing together different medicinal substances, so as to form one remedy, may boast of very ancient origin, for most of the prescriptions which have descended from the Greek physicians are of this description; the uncertain and vague results of such a practice appear also to have been early felt, and often condemned, and even Erasistratus declaimed with great warmth against the complicated medicines which were administered in his time; the greater number of these compositions present a mass of incongruous materials, put together without any apparent order or intention; indeed it would almost appear as if they regarded a medical formula as a problem in _Permutation_, the only object of which was to discover and assign the number of changes that can be made in any given number of things, all different from each other.

At the same time it must in justice be allowed, that some of the earlier physicians entertained just notions with regard to the use and abuse of combination, although their knowledge of the subject was of course extremely limited and imperfect.

ORIBASIUS[125] recommends in high terms certain combinations of _Evacuant_ and _Roborant_ medicines, and the remarks of ALEXANDER TRALLIANUS on a remedy which he exhibited in paralysis, serve to shew that he was well acquainted with the fact, that certain substances lose their efficacy when they stimulate the bowels to excess, for he cautions us against adding a greater proportion of _Scammony_ to it; many, he observes, think that by so doing, they increase the force of the medicine, whereas in fact they make it _useless_, by carrying it immediately through the bowels, instead of suffering it to remain and be conveyed to the remote parts.

In modern Europe, the same attachment to luxuriancy of composition has been transmitted to our own times: there are several prescriptions of Huxham extant, which contain more than _four hundred_ ingredients. I have already observed that all extravagant systems tend, in the course of time, to introduce practices of an opposite kind; this truth finds another powerful illustration in the history of medicinal combination, and it becomes a serious question, which it will be my duty to discuss, whether the disgust so justly excited by the _poly-pharmacy_ of our predecessors, may not have induced the physician of the present day to carry his ideas of simplicity _too far_, so as to neglect and lose the advantages which in many cases beyond all doubt may be obtained by scientific combinations. “To those,” says Sir A. Crichton, “who think that the Science of Medicine is improved by an affected simplicity in prescribing, I would remark, that modern pharmacopœias are shorn so much of old and approved receipts,[126] on account of their being extraordinary compounds, so as to be almost useless in some cases.”

In the year 1799, Dr. FORDYCE, in a valuable paper published in the second volume of the Transactions of the Medical Society, investigated this subject with much perspicuity and success: unfortunately, however, this memoir terminates with the investigation of _similar_ remedies, that is to say, of those which produce upon the body similar effects, and he is entirely silent upon the advantages which may be obtained by the combination of those medicines which possess _different_, or even _opposite_ qualities; it must be also remembered that at the time this memoir was composed by its eminent author, Chemistry had scarcely extended its illuminating rays into the recesses of physic. Under such circumstances, I am induced to undertake the arduous task of inquiring into the several relations in which each article of a compound formula may be advantageously situated with respect to the others; and I am farther encouraged in this investigation, by a conviction of its practical importance, as well as by feeling that it has hitherto never received the share of attention which it merits. “I think,” says Dr. Powell, “it may be asserted, without fear of contradiction, that no medicine compounded of five or six simple articles, has hitherto had its powers examined in a rational manner.” If this attempt should be the means of directing the attention of future practitioners to the subject, and thereby of rendering the Art of Composition more efficient, by placing it upon the permanent basis of science, I shall feel that I have profitably devoted my time and attention to the most useful of all medical subjects. “_Res est maximi momenti in arte medendi, cum, Formula in se considerata, possit esse profecto mortis vel vitæ sententia._”

PHARMACOLOGIA.|| ON THE| OPERATIONS OF MEDICINAL BODIES,| AND ON THE|
CLASSIFICATIONS FOUNDED ON THEM.

“_Medicos tandem tædet et pudet, diutius garrire de Remediis,
Specificis, et Alexipharmicis, et cæteris, nisi eorum naturam et
modum quo prosint, quodammodo ostendere et explanare possint._”

CONSPECT. MED. THEOR.

PHARMACOLOGIA.

ON THE
OPERATIONS OF MEDICINAL BODIES,
AND ON THE
CLASSIFICATIONS FOUNDED ON THEM.

Medicinal Substances are those bodies, which, by due administration, are capable of producing certain changes in the condition of the living system, whereby its morbid actions may be entirely removed, or advantageously controlled.

In adopting this definition we intentionally exclude those alimentary substances which are more immediately subservient to the support of life, and to the repair of that diurnal waste, which the exercise of its functions so inevitably occasions.

It has been generally supposed, that substances whose application does not produce any sensible action upon the healthy system, cannot possess medicinal energy; and, on the contrary, that those bodies which occasion an apparent effect in health, must necessarily prove active in the cure or palliation of disease. Under certain limitations we may perhaps venture to assent to this general proposition; but it cannot be too forcibly or too frequently impressed upon the mind of the medical practitioner, that _Medicines are frequently but relative agents_, producing their effects in reference only to the state of the living frame; we must therefore concur with Sir Gilbert Blane in stating, that the virtues of Medicines cannot be fairly essayed, nor beneficially ascertained, by trying their effects on sound subjects, because that particular morbid condition does not exist which they may be exclusively calculated to remove;[127] thus in certain states of debility, _Tonics_ may excite the system when languid, by their sympathetic influence upon the _primæ viæ_, while in a robust condition of the body, the effects of the same agents may be wholly inappreciable.

The MODUS OPERANDI of remedies, or the general principle upon which they effect salutary changes in the morbid states of the body, is involved in considerable obscurity, and has given rise to much ingenious speculation and scientific controversy. It would seem that the immediate impression of a remedy may depend upon mechanical, chemical, or vital agencies; and that the sanative impulse thus occasioned may either be Absolute, or Relative;—Primary, or Secondary;—Local, or General;—Direct, or Sympathetic;—Permanent, or Transient;—thus certain purgatives will occasion intestinal excretions in every condition of the body, and may therefore be justly considered as _absolute_ agents; while diuretics, since they generally require for their success, a certain state of the living system, may with equal truth be denominated _relative_ in their operation. That the obvious effect of a remedy may either depend upon its _Primary_, or upon its _Secondary_ and incidental operation, will at once be apparent by inspecting the diagram which exhibits the classification of diuretic medicines; the same scheme will also shew that remedies may be _local_ or _general_ in their effects, and may excite an action in distant organs, either by entering the circulating mass, and being thus brought into contact with their textures;—by occasioning an impulse conveyed through the nervous system,—or by exciting a local impression upon the stomach and _primæ viæ_, and thus arousing their energies through the mysterious medium of sympathetic[128] communication.

That certain bodies are capable of evading the assimilating functions, and of entering, unchanged, into the circulating current, either through the branches of the thoracic duct, or of the _vena portarum_, is a fact which admits of chemical demonstration; many of the alkaline salts are thus conveyed to the kidneys, and being excreted from the blood by its vessels, are to be easily detected in the urine by appropriate reagents; I have made many experiments upon this subject, and am prepared to state some results which may perhaps explain the occasional value of such bodies as medicines. Some essential oils, particular _bitter_ principles,[129] and certain colouring matter,[130] seem also capable of passing the barriers of digestion, and of circulating to the remote parts of the body; Mercury, and several of the other metals, would likewise appear, under certain circumstances, to possess a similar privilege, and the former to be able moreover to facilitate the absorption of other bodies with which it may be associated, as I shall hereafter more fully exemplify.

In some instances, the medicinal body undergoes a partial decomposition by the digestive organs, _in transitu_, by which some of its constituents escape into the circulation, while the others are completely digested, and converted into chyle; this occurs with saline compounds into which vegetable acids enter as constituents. See _Potassæ Acetas_. It is also stated in the history of Diluents, that there is reason to believe that _Water_ may under particular circumstances suffer decomposition, and transfer its elements for the formation of new compounds, furnishing _oxygen_ to some, and _hydrogen_ to others. There is likewise reason to suppose, that in particular conditions of the digestive functions, a remedy may be at once rendered inert by its entire decomposition.[131]

That an impression made upon the stomach by a medicinal agent, should be the means of exciting an action in the distant parts of the machine, will not appear extraordinary when we consider how universal a sympathy and control this central organ exercises over every function of the body; imbued with exquisite and diversified sensibilities,—subjected to the first and coarsest impressions of our various ingesta,—stretched occasionally to an enormous extent by the unrestricted indulgence of appetite,—disturbed by the passions,—exhausted by volition, and debilitated by intense thinking; in short, assailed by numerous foes from _without_, and harassed by various revolutions from _within_, can we feel surprised that the aberrations of this viscus should give origin to the greater number of maladies with which we are afflicted, or that those medicinal applications should be effective that are directed for their cure, through the medium of its sympathies?

A dose of Ipecacuan, by exciting the stomach, will abate both the force and velocity of the heart in its vital motion, and affect the whole series of blood vessels, from their origin to their most minute ramifications, as is evinced by the pallor of the skin under its operation, as well as by its efficacy in arresting hemorrhage; so the brain, when disordered by vertigo, frequently derives instantaneous relief from the administration of a tea-spoonful of æther in a glass of water. The stomach however is not in every case the medium of sympathy; a substance may excite a powerful impression upon a distant part, by the instrumentality of the nerves, without any concurrence of the stomach; thus, the _Belladonna_, by coming in contact with the _Tunica Conjunctiva_ of the eye, will occasion immediate dilatation of the _Iris_, although no other part of the system is in the slightest degree affected.

But there is yet another mode by which remedies may be made to exert a sanative effect upon particular organs of the body, through the medium of what Mr. Hunter called _contiguous_ sympathy, and whose existence appears to depend upon the mere proximity and contiguity of parts, without any relation to the distribution of the nerves; thus it is, that relief is afforded to a deep-seated inflammation, by scarifying the nearest external surface; while we know from long experience that the thoracic or abdominal viscera, when similarly affected, receive corresponding relief from the same topical use of bleeding, blistering, or fomenting.

With respect to the _Modus Operandi_ of medicines the following classification may be established.

THE PARTICULAR ORGANS OF THE BODY MAY BE EXCITED INTO ACTION, THROUGH
FOUR DISTINCT AND DIFFERENT MODES OF COMMUNICATION.

I. _By the actual contact of the appropriate remedy._

1. _Conveyed by absorption_, WITHOUT DECOMPOSITION.

_Internally._│_a._ _through the branches of the Thoracic duct_.
„ │_b._ _through the branches of the Vena
│ Portarum_.[132]

_Externally._│_c._ _through the branches of divided
│ blood-vessels_.
„ │_d._ _through the branches of Lymphatics_.[133]

2. _Conveyed by absorption_, WITH DECOMPOSITION, _by which one or
more of its constituents are developed, and pass into the
circulating current_.

II. _By an impulse conveyed through the instrumentality of the
nerves._

III. _By the sympathetic control exerted by the stomach on distant
parts._

IV. _By the operation of contiguous sympathy, or of that which is
excited by the mere proximity and continuity of parts._

And it is important to observe, that these are frequently antagonist operations, and consequently, that remedies, although they should occasion the same apparent effects, unless they act through the same medium, are not SIMILAR agents, but on the contrary, are generally medicinally incompatible with each other; for an illustration of this truth, the practitioner may refer to the observations which I have offered under the history of diuretics.

The difficulty of justly appreciating these phenomena, in every instance, has furnished a powerful objection against the validity of any classification of medicinal substances which is founded on their supposed modes of operation; and it must be acknowledged that, if we are unable to assign to remedies their primary action, or to distinguish this from their more obvious, though perhaps secondary effects, we shall frequently be compelled to place similar medicines under opposite heads, and to include those of very dissimilar characters under the same artificial division; an error which has contributed more generally to embarrass and misguide our practice than any other therapeutical fallacy, and it was the conviction of this truth which induced me to introduce the present chapter, and to impress the importance of its subject upon the attention of my practical readers.

It is probable that, in philosophical strictness, no two medicines in our Materia Medica are perfectly similar, although they recede from each other by such insensible shades of gradation that we may with practical advantage admit their parallelism; at the same time, it must be ever kept in remembrance, that _those Medicines only are practically similar, whose operations have been found by experience to continue similar under every condition of the human body; and which, moreover, owe such similarity to modes of operation which are compatible with each other, and consonant with the general indications of cure_.

The importance of admitting this proposition will be frequently illustrated in the sequel; and it may be observed in this place, that every classification in which it is not recognised as a leading principle, must be as imperfect in its execution, as it will be unjust and erroneous in its views.

Before I proceed to any farther discussion upon the present subject, it will be necessary to offer a synoptical view of an arrangement of medicinal bodies founded upon the basis of their operations, in order that I may be better enabled to illustrate the observations which it is my intention to introduce: for this purpose I shall present the reader with three different classifications of this kind; the first being that proposed by Dr. Cullen,[134] and which is now admitted to rest on principles nearly altogether false, but the investigation of which will afford many useful lessons of practical importance; the second classification is by Dr. Young;[135] and the third is that proposed by Dr. Murray,[136] which, from its simplicity and strict conformity with the views I intend to offer, will be adopted as being the most eligible for the occasion.

CULLEN’S ARRANGEMENT OF THE MATERIA MEDICA.

Medicamenta agunt in

SOLIDA. │SIMPLICIA.
„ │ _Astringentia._
„ │ _Tonica._
„ │ _Emollientia._
„ │ _Erodentia._
„ │
„ │VIVA.
„ │ _Stimulantia._
„ │ _Sedantia._
„ │ _Narcotica._
„ │ _Refrigerantia._
„ │ _Antispasmodica._

FLUIDA. │IMMUTANTIA.
„ │ Fluiditatem.
„ │ _Attenuantia._
„ │ _Inspissantia._
„ │ Misturam.
„ │ Acrimoniam Corrigentia.
„ │ _In Genere._
„ │ _Demulcentia._
„ │ _In Specie._
„ │ _Ant-acida._
„ │ _Ant-alkalina._
„ │ _Antiseptica._
„ │
„ │EVACUANTIA.
„ │ _Errhina._
„ │ _Sialogoga._
„ │ _Expectorantia._
„ │ _Emetica._
„ │ _Cathartica._
„ │ _Diuretica._
„ │ _Diaphoretica._
„ │ _Menagoga._

CLASSIFICATION OF THE MATERIA MEDICA
BY DR. YOUNG.

I. CHEMICAL AGENTS.

│1. _Caustics._
│2. _Antiseptics._
│3. _Antidotes._
│4. _Demulcents._
│5. _Diluents._