But the best provings of the pure effects of simple medicines in altering the human health, and of the artificial diseases and symptoms they are capable of developing in the healthy individual, are those which the healthy, unprejudiced and sensitive physician institutes on himself with all the caution and care here enjoined. He knows with the greatest certainty the things he has experienced in his own person.¹

¹ Those trials made by the physician on himself have for him other and inestimable advantages. In the first place, the great truth that the medicinal virtue of all drugs, whereon depends their curative power, lies in the changes of health he has himself undergone from the medicines he has proved, and the morbid states he has himself experienced from them, becomes for him an incontrovertible fact. Again by such noteworthy observations on himself he will be brought to understand his own sensations, his mode of thinking and his disposition (the foundation of all true wisdom gnwqi seuton), and he will be also trained to be, what every physician ought to be, a good observer. All our observations on others are not nearly so interesting as those made on ourselves. The observer of others must always dread lest the experimenter did not feel exactly what he said, or lest he did not describe his sensations with the most appropriate expressions. He must always remain in doubt whether he has not been deceived, at least to some extent. These obstacles to the knowledge of the truth, which can never be thoroughly surmounted in our investigations of the artificial morbid symptoms that occur in others from the ingestion of medicines, cease entirely when we make the trials on ourselves. He who makes these trials on himself knows for certain what he has felt, and each trial is a new inducement for him to investigate the powers of other medicines. He thus becomes more and more practised in the art of observing, of such importance to the physician, by continuing to observe himself, the one on whom he can most rely and who will never deceive him; and this he will do all the more zealously as these experiments on himself promise to give him a reliable knowledge of the true value and significance of the instruments of cure that are still to a great degree unknown to our art. Let it not be imagined that such slight indispositions caused by taking medicines for the purpose of proving them can be in the main injurious to the health. Experience shows on the contrary, that the organism of the prover becomes, by these frequent attacks on his health, all the more expert in repelling all external influences inimical to his frame and all artificial and natural morbific noxious agents, and becomes more hardened to resist everything of an injurious character, by means of these moderate experiments on his own person with medicines. His health becomes more unalterable; he becomes more robust, as all experience shows.

But how some symptoms¹ of the simple medicine employed for a curative purpose can be distinguished amongst the symptoms of the original malady, even in diseases, especially in those of a chronic character that usually remain unaltered, is a subject appertaining to the higher art of judgement, and must be left exclusively to masters in observation.

¹ Symptoms which, during the whole course of the disease, might have been observed only a long time previously, or never before, consequently new ones, belonging to the medicine.

If we have thus tested on the healthy individual a considerable number of simple medicines and carefully and faithfully registered all the disease elements and symptoms they are capable of developing as artificial disease-producers, then only have we a true materia medica - a collection of real, pure, reliable¹ modes of action of simple medicinal substances, a volume of the book of nature, wherein is recorded a considerable array of the peculiar changes of the health and symptoms ascertained to belong to each of the powerful medicines, as they were revealed to the attention of the observer, in which the likeness of the (homœopathic) disease elements of many natural diseases to be hereafter cured by them are present, which, in a word, contain artificial morbid states, that furnish for the similar natural morbid states the only true, homœopathic, that is to say, specific, therapeutic instruments for effecting their certain and permanent cure.

¹ Latterly it has been the habit to entrust the proving of medicines to unknown persons at a distance, who were paid for their work, and the formation so obtained was printed. But by so doing, the work which is of all others the most important, which is to form the basis of the only true healing art, and which demands the greatest moral certainty and trustworthiness seems to me, I regret to say, to become doubtful and uncertain in its results and to lose all value.

From such a materia medica everything that is conjectural, all that is mere assertion or imaginary should be strictly excluded; everything should be the pure language of nature carefully and honestly interrogated.