We may altogether conclude, that though the actions of many remedies may be partly elucidated by chemical considerations, it is impossible to account for the influence of all alike in this way. For at least the actions of nerve-medicines and of gland-medicines cannot be reasonably explained on any such hypothesis.
3. The most plausible explanations of the mode of operation of medicines have been founded on vital or general principles. By vital I mean that these theories concern actions which could only take place in the living body. They may be termed general principles, because the grounds on which they are based are neither mechanical nor chemical, but something different from both. The term dynamical has sometimes been applied to an ill-understood vital action of this sort.
Many different ideas have been broached to account thus for the action of medicines. Some, who have constructed very ingenious and plausible systems, have explained in different ways the operations of different groups of medicines. But when others have adopted a single inflexible hypothesis to account for the action of all alike, this is found, as might be supposed, to be of a very untenable character. I will now consider very briefly several such ideas; first, for the sake of clearness, dividing them into seven sections. I shall explain my meaning as I proceed. Different writers have supposed that the general operation of remedies in the cure of disease is conducted in these various ways.
| a. By degrees of stimulation. |
| b. By counter-stimulation. |
| c. By opposition. |
| d. By similar agencies. |
| e. By elimination. |
| f. By alterative actions. |
| g. By various counteractions. |
a. This idea has received the title of the "Brunonian Theory," from the name of its founder. It was promulgated by the famous Dr. John Brown at the close of the last century. He considered all diseases to arise from excessive or diminished "excitement." He was of opinion that all medicinal agents were stimulants, only that some acted so powerfully as to produce "indirect debility." These latter were to be used in sthenic, the others in asthenic disorders. But it is to be urged against this idea, that many sedatives produce no appreciable degree of "primary stimulation;" that alterative medicines are neither stimulant nor depressent; and that the actions of different therapeutic agents,—as, for example, of Opium, Mercury, and Rhubarb,—differ very much in quality, and not simply in degree, as Dr. Brown supposed. The principle, then, cannot be maintained.
b. Rasori and other Italians adopted a similar idea about the commencement of this century, only that they supposed two contrary agencies, instead of variations in the degree of the same action, like the Brunonians. Giacomini classified medicines on this plan. The two classes of medicines are termed "Hypersthenics," and "Hyposthenics,"—i. e. Stimulants, and Contra-stimulants, or Sedatives. These were to be used respectively in asthenic and in sthenic disorders. But this idea did not originate with these physicians. It prevails among the modern Hindoos, and seems to have been inculcated by certain medical writers of that nation in very remote times. (On the Hindoo System of Medicine, by Dr. Wise, 1845, p. 213.)
c. The last-mentioned idea supposes only one kind of opposition, and therefore only two descriptions of diseased action. But a much more plausible notion than that is, that each particular disease or symptom is to be cured by administering a remedy which is capable of producing a contrary state. By this contrary condition the disorder is to be neutralized. This was the maxim of Hippocrates—τα εναντια των εναντιων εστιν ιηματα—"contraries are the remedies of contraries." (De Flatibus, par. iii.) On this principle we give purgatives in constipation, opium in diarrhœa, sedatives to relieve pain, sudorifics to combat dryness of skin, etc. etc. But the rule becomes inapplicable when the cause of disease is so complicated that we cannot tell where to find a substance that shall directly oppose its agency. Besides, it cannot in theory be universally applied, for it takes no notice of treatment by evacuation or by revulsion.
d. I am brought now to an idea which is directly opposed to the last. The rule of the disciples of Hahnemann is, "Similia similibus curantur"—or, diseases are to be cured by remedies which shall produce effects similar to them. Now if this were the case, the majority of disorders would be hopelessly incurable. We know of no medicines that are capable of producing such affections as ague, small-pox, or phthisis; and when such remedies are known, their employment would certainly be singularly objectionable. Who would administer Strychnia in tetanus, Opium in congestion of the brain, or irritants in Gastrodynia? The arguments alleged in support of the theory are of the most fallacious kind. For example, it is said that diaphoretics cured the sweating-sickness, and purgatives are given with advantage in diarrhœa, on the "Homœopathic" principle. But it should be observed that the sweating in one case, and diarrhœa in the other, are the attempts of nature to get rid of the disease by eliminating a poison; and that in seconding these attempts we are availing ourselves of an agency which does not resemble the disease, but is like to the natural mode of cure. Such treatment depends, in fact, upon the principle which will have to be considered next in order.
The homœopathists would work a strange revolution in the Materia Medica.[13] Charcoal, Silica, and other substances commonly supposed to be inert, appear as remedies of wonderful efficacy. It is said that Belladonna produces a state like scarlatina, and also a condition resembling hydrophobia, and thus cures both of these disorders. Of these three propositions it is almost needless to say that all are equally erroneous. Further, an experimental trial of this principle was made by Andral on a large number of patients at the Académie in Paris, with the assistance of the homœopathists themselves. The medicines were carefully and fairly administered, but in no one instance were they successful. (Medical Gazette, vol. xv. p. 922.)
e. The idea that diseases are to be cured by assisting nature to eliminate from the system the morbid material, is probably as old as medicine. It was one of the doctrines of Hippocrates; but long even before his time it appears to have been inculcated by a certain sect of old medical writers among the Hindoos. These last were the very earliest advocates of the humoral pathology. (Dr. Wise, op. cit. p. 212.) Dr. Thomas Sydenham, born in 1624, the contemporary of Harvey, and the most illustrious of the early English exponents of the humoral system, was probably the first in this country who clearly elaborated this view of the action of medicines by elimination; which has been more or less approved, though not so universally applied, by all who have lived since his time. Agreeing with Stahl in his view of the advantages of the "expectant" treatment of diseases, he thought it better to rely on the "vis medicatrix naturæ," than to make rash or violent attempts at a cure. He maintained that what we call a disease was in fact "no more than a vigorous effort of nature to throw off the morbific matter, and thus recover the patient."[14] He proposed, therefore, that our efforts should be directed to assist nature to procure the evacuation of a poison, promoting its elimination by acting on the various secretions—as by purgatives, diaphoretics and such medicines. For he had noticed that in fevers and febrile disorders the crisis or turning-point was generally accompanied or preceded by an increase in one or more of these secretions, and he regarded this as an indication of the treatment to be pursued in all such cases. "That," said he, "appears to be the best method of curing acute diseases, which, after nature has pitched upon a certain kind of evacuation, assists her in promoting it, and so necessarily contributes to cure the distemper."[15] He further proposed, that in the treatment of chronic diseases, when nature herself was slow in procuring this evacuation, we should seek for specific medicines, by which we might assist her in doing so, and thus effectually expel the morbific matter. This theory was reasonable and natural compared to those that followed it; but it was nearly extinguished and forgotten amid the war of opinions which was subsequently kindled by the aphorisms of Boerhaave. About this time we find Dr. Pitcairn mixing up this idea with his mechanical notions, in a treatise "On the Cure of Fevers by Evacuation." Huxham also, in 1729, maintained similar principles.