Hahnemann’s first experiments in relation to the action of drugs—says Wheeler, the most recent translator of the “Organon”—were made upon cinchona bark, which at that period was universally admitted to possess remarkable power in relieving and curing “ague,” as the usual form of malarial disease was then termed. “Hahnemann’s experiment”—he goes on to say—“consisted in taking a large dose of cinchona bark while he was in good health and noting its effects upon his healthy body. To his surprise he found reproduced upon himself all the chief phenomena (and even many of the minor symptoms) of a paroxysm of ague. When the attack passed off, a second dose produced a second paroxysm, and Hahnemann was presently face to face with the fact that this drug, which so often cured ague, was capable of reproducing in his own healthy body the phenomena of ague. Like, in fact, cured like.... As soon as the cinchona experiment suggested to Hahnemann the possibility that the principle of like to like (_similia similibus_) might prove a general law of healing, he began a systematic study of the records of medicine in the search for instances.... Over and over again he found that a drug prescribed empirically had proved itself capable of curing conditions similar to those which it could produce. The records of medicine, in fact, gave plenty of encouragement to his now dawning belief that _similia similibus_ is a genuine Law of Cure.” It is at this point, as it seems to me, that Hahnemann displays the first and most important defect in his reasoning machinery. He allowed what seemed to him to be a most important and highly beneficent therapeutic truth immediately to take possession of his whole being,—indeed, to take such complete possession that, from this moment forward, throughout the remainder of his life, he was utterly unable to weigh with a calm and unprejudiced mind the various facts and considerations which ultimately relegated homoeopathy to its proper place in the medico-historical museum, alongside those hoary relics of methodism, incantations, the weaving of charms, Stahlism, Brunonianism, etc. In short, he lacked those immensely important mental characteristics which enabled Harvey to discover the more important facts relating to the circulation of the blood, and which made it possible for Jenner to place in the hands of his fellow men an effective weapon of defense against the deadly ravages of small-pox. If asked to say what are these characteristics, I would reply: A state of mind so open and so unprejudiced that it can weigh with absolute fairness all the evidence laid before it, and an imagination so clever and so fertile in resources that it is able to invent the means of reproducing at will all those phenomena which it is desirable to study more closely. These, I believe, are the characteristics which Hahnemann lacked and which are absolutely necessary for the creation of a permanently useful creed and principles of therapeutics.