The human body appears to admit of being much more powerfully affected in its health by medicines (partly because we have the regulation of the dose in our own power) than by natural morbid stimuli- for natural diseases are cured and over come by suitable medicines.
$ 31. The inimical forces, partly psychical, partly physical, to which out terrestrial existence is exposed, which are termed morbific noxious agents, do not possess the power of morbidly deranging the health of man unconditionally; but we are made ill by them only when our organism is sufficiently disposed and susceptible to the attack of the morbific cause that may be present and to be altered in its health, deranged and made to undergo abnormal sensation and function, hence they do not produce disease in every one, nor at all times.
$ 32. But it is quite otherwise, with the artificial morbific agents which we term medicines. Every real medicine, namely acts at all times, under all circumstances, on every living human being, and produces in him its peculiar symptoms (distinctly perceptible if the dose be large enough) so that evidently every human organism is liable to be affected, and as it were, inoculated with the medical disease, at all times and absolutely (unconditionally), which as before said, is by no means the case with the natural disease.
Incidentally these paragraphs have a bearing upon degree or intensity (which is potentization), upon the repetition of the dose, and upon susceptibility, things which must be known by the homoeopathic physician in order that he may be a good prescriber. We have studied potentization sufficiently to see that disease causes exist among attenuated things, the infinitesimal or immaterial substances, and thus the physician must see that curative remedy must be on the same plane. He must know why it is that he should give but one dose, and the rationale by which susceptibility is satisfied.
In contagion (and consequently in cure) there is practically but one dose administered, or at least that which is sufficient to cause a suspension of influx. When cause ceases to flow in a particular direction it is because resistance is offered for causes flow only in the direction of least resistance and so when resistance appears influx ceases the causes no longer flows in.
Now, in the beginning of disease, i.e., in the stage of contagion, there is this limit to influx, for if man continued to receive the cause of disease (if there were no limits to its influx) he would receive enough to kill him, for it would run a continuous course until death. But when susceptibility is satisfied, there is a cessation of cause, and when cause ceases to flow into ultimates, not only do the ultimates cease but cause itself has already ceased.
Hahnemann states that we have more power human beings with drugs than disease cause, for man is only susceptible to natural diseases upon a certain plane. Disease causes, existing as they do as immaterial substances, flow into man in spite of him; he can neither control nor resist them, and they make him sick. But certain changes occur and man ceases to be susceptible, and there is no longer an inflowing of cause into his economy; as a suspension has taken place, because susceptibility has ceased. Susceptibility ceases when changes occur in the economy that bar out any more influx.
But cure and contagion are very similar, and the principles applying to one apply to the other. There is this difference: in cure we have the advantages of change of potency, and this enables us to suit the varying susceptibilities of sick man. Because of these varying degrees of susceptibility some are protected from disease cause and some are made sick; the one who is made sick is susceptible to the disease cause in accordance with the plane he is in and the degree of attenuation that happens to be present at the time of contagion.