This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
There is no all-embracing and scientific system of dosage. The large intravenous dose of arsenic in the form of salvarsan and given in the treatment of syphilis, is not given upon any but the practical basis of overwhelming the spirochetes, and not as proposed in accordance with some theory of dosage. The very large hypodermatic doses of quinine given in the congestive chill of pernicious intermittent fever are given to overwhelm the malarial Plasmodia, and not to fit in with some theory. The immense doses of alkalies given in the intoxication of acute acidosis are given to neutralize acid, not on the basis of some theory of dosage.
On the other hand, the minute dose of arsenite of copper given in diarrhea is minute because the drug is very poisonous and the minute dose is enough to serve the purpose. Bryonia is given in very small doses in sore throat and pleurisy because its irritant and hydrogogue effects in large doses is toned down to merely opposing inflammatory dryness of the membranes in the small dose. Colocynth, which is a violent hydrogogue cathartic in large doses, is given in small doses in intestinal colic because temporary neuralgic pain - enteralgia, gastralgia, tenesmus - is relieved by the relaxing effect of the small dose. Thus the disagreeable symptoms are relieved; but small doses of colocynth have no specific effect upon diarrhea. In fact, nothing has a specific effect unless it removes the cause, like emetine in amebic dysentery.
Small-dose therapy, so far as it is effective at all, must be explained upon physiological grounds, as is done in the work of Dr. G. Hardy Clark, before referred to, and in my own works on materia medica, long out of print.
It may interest the reader to quote Dr. Clark, who says: "Whatever may be the reasoning applied, it is generally admitted that non-toxic doses of a drug are curative of diseased conditions similar to states induced by toxic doses of that drug." So this Homeopathic author first throws overboard nine-tenths of the Homeopathic remedies, and quotes Bartholow, Hempel, Hughes, Ringer, Wood, and others in giving the "characteristics" and "toxic symptoms" of the one-tenth remaining, practically ignoring the Homeopathic "provings"; and then he makes his "therapeutic uses" fit right in to these physiological actions and with the dosage rationally arranged without any "potentizing" or "dynamizing" involved.
One finds scattered through ancient and medieval medical literature all sorts of theories regarding dosage; no modern theories suggest anything new. After all, dosage is purely a practical question determined by matters of fact, not by theories. The "similia" theories of Homeopathy, and the "specific medication" theories of Eclecticism, one can readily see purely as reflections of old thought if he takes the trouble to consult the ancient writings. One is obliged to unload the old empiric thought, even when presented in new dress, and start anew upon as scientific a basis as one may. Practically, the minimum toxic dose is what one should remember; and he should grade down from that, according to the effect desired.