MATE'RIA ME'DICA is that branch of medical science which treats; of the articles employed in the practice of medicine, and embraces an explanation of the nature and modes of action of those substances which are had recourse to in order to restore the healthy state of the human frame when its functions or structure are impaired by disease Thus defined it comprehends both pharmacology and therapeutics. The former means an account of drugs, simple or prepared, in reference to their physical character, natural history, commercial history, che mical composition, and modes of exhibition. The latter means an exposition of the principles which should regulate their employment. The pharmacological part of the subject is sufficiently treated of under each article, as it presents itself in alphabetical order, and it is only requisite to treat here of the general principles involved in their prac tical application. For the full and satisfactory comprehension of this department, a previous knowledge of the structure of the body, or anatomy, and, above all, of general anatomy, and of the respective duties or offices performed by its component organs while in a state of integrity, or physiology, and of the various degrees of departure from these, when from any cause they become deranged in their action, or pathology, and the signs by which the morbid states are indicated, or posology, is required. These departments of science are studied only by those persons who intend to follow the medical profession, and at their hands only can a skilful employment of medicines be expected. Something however may be done for the advantage of the public by pointing out how medicines act, and in what way they prove remedial. The object of the administration of a medicine is to arrest the progress of diseased action, and to remove the consequences of its existence, that is, to restore the individual to perfect health, such as he enjoyed before the organ or organs received the impression of the morbffie cause; or where both or either of these objects cannot be accomplished, so to retard the career of the unhealthy operations, as to prolong life to the latest possible period. To improve and perfect this most im
portant branch of the healing art is the end and aim of all the other branches of medical science. The means of accomplishing this object have varied in the different stages of human civilisation, and according as different theories of the nature or cause of diseases have prevailed. Many of the medicines formerly in use were of a disgusting or repulsive nature, or of a kind devoid of any active principle, and therefore inert. Many also owed their introduction into practice to superstition, credulity, or a misapplication of the principles of natural and chemical philosophy, and have long been discarded by scientific practitioners, though frequently retained by the populace or by quacks. The medicines used in the present day are still drawn from all the three kingdoms of nature, though the animal kingdom yields few, the vegetable kingdom a considerable number, and the mineral kingdom the greatest number and generally the most active.
In general few articles produce much effect on the human frame, either in a state of health or disease, which are not possessed of marked sensible qualities, impressing the senses of smell or taste in a distinct manner. Hence bland insipid articles are mostly better fitted to furnish nourishment than medicines, being completely digested, and creating no disturbance or change of action of the vital powers of the system ; medicinal substances on the contrary do not appear to be thoroughly digested, but a portion remaining unassimilated acts in some measure as a foreign body, and produces a stimulant or alterant effect on the vital power. Many medicines are indeed absolutely poisonous if given in large doses, or where no diseased state of the system requires their administration. For disease often gives to the system a power of sustaining the action of a dose of medicine which would produce serious disorder if given to a person in health ; the morbid state of the system seeming to act as an antidote to the medicine, while the medicine acts as an antidote to the disease--health being the result of their neutralising power.