_Ord. 2. Antisyphilitics._ Mercurials; Preparations of Gold; Iodide of Potassium; Sarsaparilla (?). _Ord. 3. Antiscrofulitics._ Iodine; Bromine; Chlorine; Iodides and Bromides; Potash. _Ord. 4. Antiarthritics._ Colchicum; Nitro-hydrochloric Acid; Lemon-juice. _Ord. 5. Antiscorbutics._ Citric Acid; Lemon-juice; Fresh Vegetables; Salts of Potash (?). _Ord. 6. Antiperiodics._ Arsenious Acid; Arsenite of Potash; Alum; Chloride of Sodium. _Ord. 7. Anticonvulsives._ Preparations of Arsenic, Silver, Zinc, Lead, and Copper. _Ord. 8. Antisquamics._ Preparations of Arsenic; Sulphur; Pitch. Under each head I have given the most important of those medicines which I conceive to act on the Catalytic principle. Other medicines may cure some of these disorders, or at least alleviate them; either by acting as Restoratives, as in the case of arthritic and of periodic disorders; or by influencing the nervous system, which plan may be effectual in some convulsive affections. The prefix _Anti-_ involves a principle. These medicines produce certain actions which are _contrary_ to diseased actions, inasmuch as they neutralize them, and cannot subsist with them. It is granted that in some cases the actions may appear similar in some respects. But this merely shows that they move, as it were, in the same sphere, for else one of them could not meet the other. However the operation of a medicine may sometimes seem to resemble that of a disease, it is always in effect contrary to it. The similarity is of a kind which does not concern us. An acid and an alkali are so far similar, that they may both produce heat when mixed with water, and both prove corrosive and destructive to organized tissues; but they are practically contrary, and when brought together they neutralize each other. Let us now proceed to the minor propositions.