§ 138
All the sufferings, accidents and changes of the health of the experimenter during the action of a medicine (provided the above condition [§§ 124-127] essential to a good and pure experiment are complied with) are solely derived from this medicine, and must be regarded and registered as belonging peculiarly to this medicine, as symptoms of this medicine, even though the experimenter had observed, a considerable time previously, the spontaneous occurrence of similar phenomena in himself. The reappearance of these during the trial of the medicine only shows that this individual is, by virtue of his peculiar constitution, particularly disposed to have such symptoms excited in him. In this case they are the effect of the medicine; the symptoms do not arise spontaneously while the medicine that has been taken is exercising an influence over the health of the whole system, but are produced by the medicine.