The third doctrine, that Psora, the other name of which you remember, is the cause of the great majority of chronic diseases, is a startling one, to say the least. That an affection always recognized as a very unpleasant personal companion, but generally regarded as a mere temporary incommodity, readily yielding to treatment in those unfortunate enough to suffer from it, and hardly known among the better classes of society, should be all at once found out by a German physician to be the great scourge of mankind, the cause of their severest bodily and mental calamities, cancer and consumption, idiocy and madness, must excite our unqualified surprise. And when the originator of this singular truth ascribes, as in the page now open before me, the declining health of a disgraced courtier, the chronic malady of a bereaved mother, even the melancholy of the love-sick and slighted maiden, to nothing more nor less than the insignificant, unseemly, and almost unmentionable ITCH, does it not seem as if the very soil upon which we stand were dissolving into chaos, over the earthquake-heaving of discovery? And when one man claims to have established these three independent truths, which are about as remote from each other as the discovery of the law of gravitation, the invention of printing, and that of the mariner's compass, unless the facts in their favor are overwhelming and unanimous, the question naturally arises, Is not this man deceiving himself, or trying to deceive others? I proceed to examine the proofs of the leading ideas of Hahnemann and his school. In order to show the axiom, similia similibus curantur (or like is cured by like), to be the basis of the healing art,--“the sole law of nature in therapeutics,”--it is necessary, 1. That the symptoms produced by drugs in healthy persons should be faithfully studied and recorded. 2. That drugs should be shown to be always capable of curing those diseases most like their own symptoms. 3. That remedies should be shown not to cure diseases when they do not produce symptoms resembling those presented in these diseases. 1. The effects of drugs upon healthy persons have been studied by Hahnemann and his associates. Their results were made known in his Materia Medica, a work in three large volumes in the French translation, published about eight years ago. The mode of experimentation appears to have been, to take the substance on trial, either in common or minute doses, and then to set down every little sensation, every little movement of mind or body, which occurred within many succeeding hours or days, as being produced solely by the substance employed. When I have enumerated some of the symptoms attributed to the power of the drugs taken, you will be able to judge how much value is to be ascribed to the assertions of such observers.