Nature heals, physicians treat - is a truth of old that is constantly forgotten: always by the patient, who expects the patent medicine or the family doctor to cure her; frequently by the physician, who is often persuaded, against his better judgment, to believe in the supernatural when the mysteries of drug action are involved. A few propositions concerning the general action of the human body in its endeavor to heal itself may not be out of place in an introduction to a work on the practice and art of aiding nature's forces in the treatment of abnormal conditions.

It is a difficult task to express, in a few phrases, the general causes of disease, but the following general agencies may be considered:

1. Trauma, whether the result purely of accident, or brought about in the general struggle for existence.

2. Parasites, both microscopical and macroscopical, acting within and without the body.

3. Poisoning from plants and animals, broken down and decomposed food-stuffs, and poisonous gases taken into the respiratory tract.

4. Bad hygiene, unwise modes of living, including faulty nutrition, faulty modes of dress, eating, and housing, use or abuse of certain organs or their lack of use.

5. Heredity. - Here would be classified not only the directly transmissible diseases, as syphilis, but also those constitutional dyscrasiae that conduce to premature break-down of some part of the human body.

In order to combat these various agencies the individual organs have developed a system of natural cure methods ("natural therapeutics") that are of interest. These may be summarized briefly, following Kobert, in part, as:

1. Healing by regeneration. Among the lower animals the regeneration of a lost member is not infrequent, but in man it is unusual. In a sense, however, the healing of wounds as a part of the inflammatory reaction is analogous to this process in the lower animals. The hypertrophy of one kidney, compensating for the loss of the other, and the establishment of a collateral circulation are illustrations of what Bachmann, in 1894, pointed out as the law of equivalent compensations.

2. Healing may be brought about by the exercise of an organ. Thus, the old-fashioned system of exposure to wet and weather develops, by exercise of the skin, an increased resistance to agencies that otherwise might react harmfully on the organism.

3. In the struggle against parasites it would appear that the body had developed an extensive array of protective agencies. Thus, antiseptic substances in the saliva, gastric juice, and bile are simple instances of this protective power against parasites from the outside. The doctrine of phagocytosis embodies the principle of the action of the white blood-cell in its office as a protective agent. In the body-fluids are found alexins, antitoxins, immunizing pro-teids that protect from the actions of poisons which may develop as a result of the life activities of these parasites should they obtain a foot-hold within the body - or even protect from poisons developed in the course of disturbed metabolism. Fever, so frequently regarded as an adverse sign in disease, undoubtedly serves in large part as a means of protection of the body - by killing the agents that have induced the rise in temperature.

4. Healing from certain poisons is brought about by vomiting and diarrhea, by rapid elimination through diuresis, or by excessive perspiration. Within the body a most interesting series of changes often takes place - thus, splitting up of poisons, their oxidation or conversion, or even fixation, into non-toxic products is a constant phenomenon. Thus even so powerful an alkaloid as morphine is said by Faust to be in part oxidized and perhaps used as a foodstuff. The chemical changes that take place in the liver have here their most potent activities, and the pathological chemistry of the twentieth century promises to throw much light on these complicated problems. Poisons also are compensated for by the process of adaptation (habituation), and are frequently rendered inert by the development of specific antitoxic substances. Thus specific anti-morphine bodies have been developed in the blood of some of the lower animals.

5. The physiological process of rest is an expression of nature healing. Loss of appetite is the indication not to eat. Pain calls for rest.

6. Healing by the casting off of a portion of the organism is a process of nature healing widely made use of in diseases among plants and the lower animals. Abscess formation, the limiting, by fibrinous exudates, of intraperitoneal irritants, and spontaneous gangrene of the extremities are well-recognized examples of such a type of nature's healing.

Treatment is something apart from healing, and in its broad sense comprises all those means, psychical or physical, which the practiser of the healing art has at his command by which he can hope to alter an abnormal condition in the individual he is called on to treat. Thus, nature calls into play the highest of her gifts, intelligence, to aid her in the work of self-preservation, and it is the function of the text-book to aid, in so far as it is able, to train that intelligence in the facts that experience has proved of value -in the present instance, in the fields of materia medica, pharmacodynamics, and therapeutics.

Pharmacology, from the broad point of view, is the science of drugs, and includes the various fields of medical botany, medical zoology, pharmacognosy, pharmacodynamics, and pharmacy. Within recent years, however, following the German school, its meaning has been restricted and made equivalent to pharmacodynamics, or the study of the effects of physical or chemical agencies on living organisms. It is in this sense that it is used in this work.

Materia Medica is the study of the source, constituents, chemical and physical characters of the organic and inorganic materials used for drugs in the practice of medicine.