The Action of Medicines in the System / Or, on the mode in which therapeutic agents introduced into the stomach produce their peculiar effects on the animal economy

by Frederick William Headland

Phosphorus is a Stimulant. In small doses it quickens the pulse. It somewhat heightens the mental activity. It is said also to have an aphrodisiac operation, due to its powers as a cerebral excitor. Volatile oils possess a certain influence over the functions of the brain, as well as those of the organic nerves. Cajeput oil has been used in Hysteria; employed to control various spasmodic movements; and administered in Typhoid fevers and Asiatic Cholera, to communicate nervous power. The fetid gum resins are well known as Antispasmodics. The spasms which these medicines relieve are due to a fault in the nervous polarity, commencing generally in the brain or nerve-centres,—and are more or less subdued by general stimulators of the nervous functions. Copaiba, an oleo-resin, may cause a general febrile condition, accompanied with headache,—when given in large doses.

So obvious is the cerebral power of some volatile oils, that Turpentine, in large doses, has been known to produce inebriation. It is not generally used for its Neurotic powers, but as a Purgative or a Diuretic; or else it might have been classed among Inebriant Narcotics. I have enumerated it above among volatile oils. It may be regarded as transitional between true Stimulants and Narcotics.

Ergot of Rye is another medicine which has a double action. It is used as a Special Stimulant to the Uterus; but it is also a Narcotic to the brain.

Most General Stimulants are without any marked influence on the mind; but stimulate the organic and merely animal function of the brain, and of the Sympathetic nerve throughout the system.

Concluding that General Stimulants have all more or less the power of exalting nervous force in general, we have still to consider some other questions relating to their action.

It is maintained by some that Stimulants have simply the power of calling forth the nervous force which already exists in the system, and that they cannot create any more in addition to this. But if this were the case, then the reaction, or subsequent failure of nervous power, ought to be exactly equivalent to the first temporary increase of that power; assuming this increase to have been simply abstracted from the natural resources. But we do not find it to be so. The reaction from the effect of a Stimulant is always very slight, and often quite imperceptible.

And there seems to be no à priori reason why we should not actually cause nervous force to be generated. We know that a galvanic current, or even a mechanical cause, may induce it to be suddenly and powerfully manifested. I believe that a Stimulant is able actually to produce nervous action; perhaps by an irritative operation upon nerve-fibre. So by continually repeating the dose of a Stimulant, as Ammonia or Brandy, it is possible to maintain the circulation and nervous energy at a certain level, without the occurrence of any reaction for a considerable period.

But we must take care not to confound nervous force with vital force. The former may be very much increased, as in high inflammatory fever, without a corresponding increase of the latter. The advantage of a stimulant is regulated by this rule. When there is a failure in vital energy, no Stimulant will serve to prolong life, for it cannot communicate fresh vital power. But there may be no such failure of vital energy, and yet a sudden or accidental deficiency of nervous force may serve to peril the continuance of health, or even the tenure of life. For a certain degree of this nervous force is necessary both for life and health. When it is diminished, all the functions must suffer; when it fails entirely, the circulation must stop, and death ensues. It is in these cases that a Stimulant medicine is appropriate. It does not do good by communicating vital energy, but by remedying the want of nervous action, by which want the manifestation of the vital energy is subdued. This must always be borne in mind when the applicability of Stimulants is under consideration.

Some writers have complicated the subject by classing as Stimulants all medicines which tend, directly or indirectly, to communicate vital strength; as Tonics, and remedies which counteract morbid depressing causes. This is in direct contradiction to the rule given above. True Stimulants are only of use by counteracting that failure of nervous force which hinders the manifestation of the vital strength which is stored up somewhere in the system. For I have just observed, that to exalt nervous force is not necessarily to exalt vital force, but that any thing which tends to destroy the former must at length repress and extinguish the latter.

The above considerations apply to the action of these Stimulants on the powers of the system generally. But they may act locally. Thus in moderate doses they promote digestion, by acting on the nerves of the stomach and intestinal canal. They increase most of the secretions in passing through the glands in the blood. In both cases they exalt nervous force; but in the latter case their action is of a particular nature, and will be treated of when they are considered under the title of Eliminative medicines.