In 1790, while engaged upon the translation of the `Materia Medici' of Cullen, he was struck with tho different explanations given of the mode of operation of Peruvian hark in intermittent fever; and dis satisfied with them, he determined to try its effects upon himself Finding that powerful doeca of this substance produced symptoms strikingly analogous to those of that form of intermittent fever for which it was an acknowledged specific, ho determined to try further experiments with other medicinal substances upon himself and upon some medical friends. He obtained similar results : that is. he pro duced by these agents factitious or medicinal disorders resembling the diseases of which they were esteemed curative ; and thus, the first down of the law of Sirnilia Similihus ' gleamed upon him. In a work ascribed to Hippocrates (Ed. Basil. ap. Froben., 1538, p. 72) a similar doctrine was enunciated, and the same doctrine has since found advocates In many eminent medical writers ; but Hahnemann was the first who assumed it to be the guiding principle in Therapeutics, and supported his position by a series of experiments. Confident that he had discovered the long-sought-for law, he assiduously pursued his proving of medicines, and adopted the new principle in the treatment of his patients with (according to his own testimony and that of his disciples) a success fully commensurate with the limited means then nt his disposal. Thus encouraged, he ventured in 1796 to address a paper to Hufeland's 'Journal,' in which be announced his new dis covery to the medical world, pointed out the defects of the ' Materia Medics'' as then constituted, and the necessity of its reconstruction upon the basis of pure experiment; at the same time he earnestly invited the c6-operation of his medical brethren. The attention of the German physicians was then deeply engaged in the investigation of the Brunouian theory, and Hahnemann's suggestions were coldly received.
In 1801 he published a short treatise on the efficacy of Belladonna in the prevention and cure of scarlet fever, and affirmed that its curative properties were based upon the homoeopathic law. In 1805 ho pub lished the results of a number of experiments in a work In two volumes, entitled Fragwenta de Viribus Medicamentorum pogitivis give obviis in Corpora Sapp; and in the same year his ' Medicine of Experience,' in which he still more strongly expresses his objection to the old system of medicine. In 1810 ho brought out his great work, tho 'Organon of the Healing Art,' in which he developed his new system of treating disease; and for the first time gave it the name of Homosopathy,' by which it has since been distinguished. Iu 1811
the first part of the Materia Medica Pura ' was published, six volumes of which appeared in succession till it was completed in the year 1821, since which time several other editions have been published.
In the year 1812 he returned to Leipzig, where he was appointed Magister Legens. To prove his qualifications for this chair, he wrote an excellent treatise on the hellebore of the ancients, Dissertatio historico-medica de Helleborismo Veterum.' At Leipzig he had an extensive practice, and was assisted by a great number of friends and pupils in the proving of his medicines. The apothecaries of that city however rose against him, and appealing to an old law long dormant, that forbade a physician to dispense his own prescriptions, they eventually, after some litigation, succeeded in 1820 in obtaining a decision in their favour. Hahnemann, unwilling to risk his own reputation and that of his system upon medicines prepared and dis pensed by individuals avowedly hostile to his medical tenets, had determined to retire from practice, when the Duke of Anhalt Cbthen offered him an asylum in his dominions, with the enjoyment of those privileges of which he had been deprived at Leipzig. It was during his sojourn at Cothen, in the year 1828, that he published in four volumes his work on 'Chronic Diseases, their Peculiar Nature, and Homoeopathic Cure.' In 182g the disciples and admirers of Hahne mann caused a bronze medal to be struck to mark their attachment to the new system and their esteem for its founder. It bore on the face the head of Hahnemann, with the inscription, 'Samuel Hahnemann natus 3lisenm D.X Aprilis lawny. Doctor mat, Erlangen D.X Augusti MDCCLXXIX.' On the reverse, in the centre, Similia Similibus the inscription, Medieinse Homceopathicte Auctori, Discipuli, at Amici, lax Augusti MDCCCXX1X.' His adherents had at this period greatly increased, and he enjoyed a very extensive practice among his own countrymen and foreigners.
Having been a widower for some years, he married in 1835 a French lady, Melanie de Herville, who had visited COthen for the benefit of his advice, and at her desire he !moved to Paris. In commemoration of his arrival in the French capital, an admirably-executed medal by David was struck in bronze, silver, and gold, bearing on its face the head of Hahnemann. He remained at Paris in the active exercise of his profession, and surrounded by numerous followers of his system of all nations, till the time of his decease, which took place on tho 2nd of July 1843, in the eighty-ninth year of his age.