This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Syn. Stimulant Narcotics.
These are medicines which, to a stimulant influence over the circulation and nervous system generally, add a peculiar power over the special functions of the brain, as evinced, in their higher grades of action, by delirium and stupor. From their stupefying property, they have been called narcotics, derived from the Greek verb which signifies to be or become torpid, dull, or stupid. But I do not think that the possession of this property is a sufficient basis for the formation of a class; for it belongs to medicines quite different and even opposite in their modes of operation, and therapeutic character. Thus, both opium and digitalis are capable of producing stupor; but the former is directly stimulant, and the latter directly sedative; and so opposite are they in their effects upon the system, that the former is one of the best instruments for controlling the excessive action of the latter. Besides, certain medicines, as alcohol and ether, have been generally excluded from the narcotics. though they act upon the brain with an energy scarcely inferior to that of any acknowledged substance of the class, and are both powerfully stupefying agents. I have thought it best, therefore, to abandon the old class of narcotics, and to arrange the medicines composing it according to their more important affinities; placing in separate categories the stimulating and the sedative, and merely retaining the word narcotic to express a quality, as we employ the terms anodyne, soporific, etc.
The only properties in which all the medicines of this class agree are those stated in the definition. In all other respects they differ among themselves, and some of them very greatly. In the first place, they differ very much in the degree of their general stimulant power. In this respect, alcohol and ether may be placed at one end of the scale, and henbane at the other; the two former medicines being among the most powerful stimulants in our possession, the latter having no more of this property than barely sufficient to justify its position in the class. Secondly, they differ in the degree in which they relatively affect different organs or functions. Thus, if we compare alcohol and opium, we shall find that the former has a greater proportional influence in stimulating the heart and arteries, the latter in stupefying the brain. Thirdly, they differ in the manner in which they affect precisely the part or organ upon which they operate. The symptoms of cerebral disturbance produced by alcohol are unlike those resulting from the use of opium; and both differ materially in this respect from belladonna. Fourthly, there is, for the most part, in each one of them, a characteristic mode of affecting some function apart from their general action as cerebral stimulants. Thus, opium produces constipation of the bowels, hyoscyamus often acts as a laxative, and belladonna occasions a characteristic dryness and irritation of the fauces.
In some measure, this difference of action may be accounted for by supposing, that the influence of the several articles of the class is directed more especially to some one portion of the brain rather than to another, though all parts may be more or less affected. Thus alcohol, from its peculiar influence on the voluntary movements, and the powerful stimulation it exercises upon the sexual propensities, may be supposed to operate more especially on the cerebellum; opium, from its great stupefying power, to act on the cerebral lobes with peculiar energy; belladonna, from its property of impairing vision, to have a more immediate influence on the optic thalami or corpora striata. But too little is yet known of the precise functions of different portion's of the encephalon, or of the phenomena by which influences upon them respectively could be recognized, to justify any very decided opinion upon the affinity which the several cerebral stimulants may have for particular parts of that structure.
The difference in the effects of cerebral stimulants on the pupils is a striking point of diversity between them, which has attracted much attention, but which only recent discoveries in relation to nervous action enable us partially to explain. Thus, while opium often contracts the pupil, belladonna much more strikingly produces dilatation. This has been considered as evincing an essential antagonism between those two narcotics. It only proves that, in reference to this particular effect, they either act differently on a special nervous centre, or in like manner on different nerve centres with which these phenomena are connected; while, as regards their general action, there may be no antagonism whatever. Thus, supposing the radiating fibres of the iris to be excited by the sympathetic nerve, and the circular by nerves from near the base of the brain, as the third or fifth pair, and these forces to balance each other in the normal state, it follows that whatever excites the sympathetic centre in the medulla oblongata, or paralyzes the basic centres referred to, will produce dilatation of the iris, while a paralyzing influence on the sympathetic centres, or one of an excitant character on the others, will equally produce contraction; so that, while two cerebral stimulants differ in their mode of affecting these special centres, they may correspond in their effects on the remainder of the cerebro-spinal axis, or while one acts on one of the centres, and the other on the other, they may both act in the same manner, and with the same effect, that is, may both be excitant, or both depressing.
Though differing so much among themselves, there are affinities between certain articles of the class, which might serve to arrange them in subdivisions, having, to a considerable extent, a common therapeutic basis. They might thus be arranged in groups, of which one would contain alcohol and ether, another opium, extract of hemp, lactucarium, and hyoscyamus, and a third belladonna and stramonium; the other individuals of the class remaining isolated. By considering them successively according to these relations, we may, sufficiently for practical purposes, fix in the recollection of the student the resemblances referred to.
Before proceeding to a general account of the mode of operation, and therapeutic properties of the class, it will serve to prepare the way, if we dwell for a short time on certain peculiarities in cerebral pathology, which, if not understood, will inevitably lead into great confusion. It is a well-established fact, that opposite morbid conditions of the brain, or parts of it, express themselves by similar phenomena; and the law probably holds true of the nervous centres universally. Pain and other morbid sensations, spasm and other forms of irregular muscular action, delirium partial or complete, mild or severe, chronic or acute, and every grade of stupor, from slight drowsiness to the deepest coma, may all arise, and frequently do arise, from the two opposite affections of irritation and depression of the cerebral centres. For proofs of this, and for an explanation, which, in the opinion of the author, may serve to reconcile the apparent contradiction, readers are referred to the article on functional diseases of the brain in his work on the Practice of Medicine. It would occupy more space than could be spared to repeat them here. But the application of this fact to the subject now before us is of great practical importance. From a certain similarity in their obvious effects, medicines essentially different in character have been associated together in the minds of writers and practitioners, and been considered as nearly identical in nature, so that they might be interchangeably employed under the same circumstances, without disadvantage.Now, as opposite morbid causes, acting on the same cerebral centres, may produce the same morbid phenomena; as, for example, insufficiency and excess of blood in the brain may either of them produce delirium, coma, and convulsions; it follows necessarily that medicines, which in excess are always morbid causes, may also, though really opposite in character, give rise to closely resembling, if not identical symptoms. Thus, of the medicines usually ranked together as narcotic, because they produce the common effect of stupor, some operate as direct stimulants, others as direct sedatives to the nervous centres; and it will be readily understood that, if such medicines are used remedially, under the impression that they are identical in character, the most serious consequences might ensue. Opium is stimulant to the nervous centres, aconite is sedative : but both in over-doses are capable of producing coma. In a case of active congestion of the brain, in which the latter may be useful, the former could do only injury; and vice versa. To administer them, therefore, indiscriminately, because of their common stupefying effect, would be a grievous error. But a case more in point, because there is reason to think that attention has not yet been sufficiently called to it, is that of ether and chloroform. Both of these are powerful anaesthetic agents; and, under the impression that their mode of action is essentially identical, they have been used and recommended in similar cases, with little discrimination. The one is, in fact, a most energetic cerebral stimulant. the other an equally powerful cerebral sedative : is it, therefore, surprising that, used indiscriminately, one of them at least should have occasioned so fearful an amount of mortality? The importance of guarding against such a therapeutic error is, it appears to me, an irrefragable argument in favour of the division I have made of the narcotic medicines into classes, founded not on phenomena which are readily misinterpreted, but on their real physiological influence on the brain, and the general system.