Every one has some idiosyncrasy or peculiar susceptibility to certain influences. It is for this reason that only a few persons out of the many are affected when exposed to the infinitesimal noxia that cause disease. The sensitiveness of a sick man to the homoeopathic similimum is wonderful, while a remedy that is not homoeopathic to this condition may be given in massive doses with little effect. No one can be made sick in a lasting way by drug to which he is not susceptible. This fact may serve to explain how at times a high potency of the same drug with which a person is poisoned proves curative. In other words, in such a case the patient was poisoned because he was already sick or susceptible and needed that remedy, but the drug not being on the same plane as his susceptibility poisoned instead of curing him.
Kent also suggests that patient repetition of a crude drug may bring about susceptibility to it, and that after a time the merest inhalation of it may produce its effects.- (Hom., Phys., Sept. 1889).