§ 111
The agreement of my observations on the pure effects of medicines with these older ones – although they were recorded without reference to any therapeutic object, – and the very concordance of these accounts with others of the same kind by different authors must easily convince us that medicinal substances act in the morbid changes they produce in the healthy human body according to fixed, eternal laws of nature, and by virtue of these are enabled to produce certain, reliable disease symptoms each according to its own peculiar character.

§ 112
In those older prescriptions of the often dangerous effects of medicines ingested in excessively large doses we notice certain states that were produced, not at the commencement, but towards the termination of these sad events, and which were of an exactly opposite nature to those that first appeared. These symptoms, the very reverse of the primary action (§ 63) or proper action of the medicines on the vital force are the reaction of the vital force of the organism, its secondary action (§§ 62-67), of which, however, there is seldom or hardly ever the least trace from experiments with moderate doses on healthy bodies, and from small doses none whatever. In the homoeopathic curative operation the living organism reacts from these only so much as is requisite to raise the health again to the normal healthy state (§ 67).

§ 113
The only exceptions to this are the narcotic medicines. As they, in their primary action, take away sometimes the sensibility and sensation, sometimes the irritability, it frequently happens that in their  secondary action , even from moderate experimental doses on healthy bodies, an increased sensibility (and a greater irritability) is observable.