This section is from the book "A Compend Of The Principles Of Homoeopathy", by William Boericke. Also available from Amazon: A Compend of the Principles of Homoeopathy as Taught by Hahnemann.
Violent cases of poisoning never yield a profitable symptomatology, on account of the violent invasion by foreign destructive agents. The organism throws it off by all routes outward and away from its distinctive life, hence vomiting, diarrhoea, convulsions, etc., common to all kinds of poisoning. On the other hand, the records of poisoning give us the ultimate action, the tissue and organic changes that the provings can only indicate, and thus they illustrate and interpret the provings.
The provings with comparatively small doses avoid these violent, crude and extreme effects, and instead of producing them, rather indicate them by mild disturbances. We thus obtain the finer and more characteristic action, and thus a much more utilizable picture of drug effects. Fortunately, the bulk of the homoeopathic Materia Medica is made up from this source. The symptoms obtained from toxicological observations and from provings are also called pathogenetic symptoms, and the full record, in the order of their development, is called the drug's pathogenesis. The "Cyclopaedia of Drug Pathogenesy" gives these in their fullest and most accurate form.
In the evolution of the homoeopathic Materia Medica, another class of symptoms not bearing the aristocracy of origin, characterizing pathogenetic symptoms, were introduced, so-called clinical or curative symptoms. This source was almost unavoidable, so long as drug provings on the healthy were limited in number and extent. The symptomatology of most of the great constitutional or anti-psoric remedies consists, in large part, of such clinical symptoms. They are such symptoms as disappear after administering a remedy, and which are not found among the pathogenetic effects, so far as the provings have been made; but, wherever genuine, there can be no doubt that they are possible pathogenetic symptoms, could we have full and accurate provings. In this way the homoeopathic Materia Medica has been enlarged, not always wisely, however; for, in order to discover them amidst the symptoms of the disease in a patient, much discrimination and training are required. Hahnemann rightly says that this is a "subject for the exercise of a higher order of inductive minds, and must be left solely to masters in the art of observation". But, when found, they must be used tentatively and cautiously until verified in practice. Only then can they be admitted by the side of the true pathogenetic symptoms and form a legitimate addition to the Materia Medica. Some of the greatest characteristics and guiding symptoms belong to this class. These clinical symptoms have been excluded from the "Encyclopaedia of Materia Medica" by T. F. Allen, and, of course, cannot have any place in the "Cyclopaedia of Drug Patho-genesy"; but they are included in full in Hering's "Guiding Symptoms" and in all manuals and textbooks of Materia Medica. In some of these they are designated by a distinguishing mark, usually O, but in most of the later works even this caution is disregarded.