By Materia Medica we understand a knowledge of the remedies employed in medicine. This knowledge may be subdivided into several divisions: Materia Medica proper, Pharmacy, Pharmacology, and Therapeutics.

By Materia Medica proper we mean an acquaintance with the remedies used in medicine, the places whence they come, the crude substances, plants or animals which yield them, the methods by which they are obtained, and the means of distinguishing their goodness or purity, or of detecting fraudulent adulteration.

By Pharmacy we mean the methods by which drugs are prepared and combined for administration.

By Pharmacology we mean a knowledge of the mode of action of drugs upon the body generally, and upon its various parts. It is of comparatively recent growth, but is now one of the most important subdivisions of Materia Medica.

By Therapeutics we understand a knowledge of the uses of medicines in disease.

Therapeutics may be either empirical or rational. By empirical we mean that drugs are triad haphazard, or with little knowledge of their action in some cases, and, being found successful, are again administered in other cases which seem to be similar.

Perhaps the best example of the empirical use of a remedy is that of quinine in ague. We do not know with certainty what the pathological conditions are in this disease, nor how quinine acts upon them; all we know is that it has proved useful in cases of ague before, and therefore we give it again.

Rational therapeutics consists in the administration of a drug because we know the pathological conditions occurring in the disease, and know also that the pharmacological action of the drug is such as to render it probable that it will remove or counteract these conditions.

Rational therapeutics is the highest branch of medicine. Its advance is necessarily slow, because it is based upon pathology on the one hand and pharmacology on the other, and both of these rest upon physiology, which in its turn rests upon physics and chemistry. It is only with the development of the fundamental sciences that those which rest upon them can grow; and when we consider that chemistry as a science is not much more than a hundred years old, and when we see the advances it has already made, we cannot but be hopeful for the future of therapeutics.

Occasionally we hear the question asked, 'What is the use of knowing the action of all sorts of drugs upon the different parts of the animal body, and what is the use of knowing the alterations in the muscles, vessels, or nerves which occur under pathological conditions, seeing that in many instances such a knowledge cannot be utilised for the treatment of disease ? ' As well might we ask, on seeing a half-built bridge, 'What is the use of laying the foundations and building the piers, seeing no one can walk across from one end to the other ?'

As an example of rational therapeutics, we may take the use of nitrite of amyl in certain forms of angina pectoris. The obvious symptoms in this disease are intense pain in the region of the heart, and fear of impending death. Sphygmographic tracings of the pulse taken during this condition show that the tension within the heart and vessels begins to increase as the pain comes on, and reaches such a height that the heart can barely empty itself. Observations on animals have shown that nitrite of amyl lessens the tension of the blood in the vessels; and we therefore give it in angina pectoris with the expectation that it will diminish the tension and remove the pain, and we find that it succeeds.

But this example shows us only the first stage of rational therapeutics. We have removed by a remedy the pathological condition which immediately gives rise to the pain and danger of the patient, but the antecedent alterations of the heart, bloodvessels, and nervous system, which led to the occurrence of the pain, are unaltered by the remedy. In order that our therapeutics should be completely successful, we must seek still further for something which will restore the circulation and nervous system to its normal condition and bring the patient back to a state of perfect health.

Sometimes we are able to do this. For example, we occasionally meet with a kind of pain in the cardiac region which closely resembles angina pectoris, and is probably a form of it. Acting on the general principle that pain is due to irritation somewhere, though not necessarily at the place where the pain is felt, we seek for the irritant. We find swelling and tenderness over the sternum at the junction of the manubrium and the body, and we look upon this as the irritant which is exciting the cardiac pains. Judging this swelling to be syphilitic, we give iodide of potassium; the swelling subsides, and the angina-like pain completely disappears.

But sometimes it is impossible to remove the cause of the disease, and all that we can do is to alleviate symptoms. The organic changes which have occurred in the course of the disease may be so great that we can hardly hope that any remedy will ever be discovered sufficiently powerful to remove them. We must therefore try to prevent them.

Preventive medicine, or prophylaxis, is daily becoming more important, and, possibly before the end of this century, medical men will be employed more to prevent people from becoming ill than to cure them when disease has become fairly established.

This may at least be the case in regard to the contagious and infectious diseases, which attack people as it were by accident, and are totally unconnected with their ordinary work or pleasure. It is too much to hope that other diseases which depend upon hereditary tendencies, overwork, or over-indulgence, will disappear, for there can be little doubt that men in the future will, as in the past, knowingly sacrifice, not only their health, but their life, to ambition, duty, or pleasure.

The advance of this branch of medicine has been greatly aided by the recent increase in our knowledge of the life-history of microbes and their action in causing disease. Our power to prevent disease will become greater when we know accurately the action of various drugs in destroying these microbes or preventing their growth.

Pharmacology has made such rapid advances of late years that it is exceedingly difficult for many men who are engaged in practice to understand thoroughly either the methods by which it is studied, or its results. Many students also, although they may be able to pass a good examination in physiology, find it difficult to apply their physiological knowledge to pharmacology; and therefore in discussing the action of drugs upon the various functions of the body, I have sometimes entered more fully into the physiology of those functions than may seem to some at all either necessary or advisable.

In discussing pharmacological questions, we are accustomed to speak of the action of a drug on the body or on its various parts; but we must remember the effect produced is not due to a one-sided action - that what we actually mean is the re-action between the drug and the various parts of the body.

In some instances we know that the drug itself is changed in the body, as well as the function of the body modified by the drug; and even in those cases where the drug itself is eliminated from the body apparently unaltered, it is probable that it has entered into various chemical combinations within the body while circulating in the blood or present in the tissues.