It would seem that Ague and its kindred disorders are capable of being combated and cured in two different ways; by Restoratives, such as Quina, which appear to supply the blood with a certain needful material; or by Catalytics, as Arsenious acid, which operate by antagonizing a morbid action, which is either the cause or the result of the blood-disease. I have given my reasons for ranking Quina and Tonics among Restorative medicines. The following are the principal grounds for which Arsenic is included among Catalytics. It is unnatural to the blood, and is at length excreted from the system. It acts as a poison; and is able to work out in the blood a certain process of its own. It has no sudden action on the nervous system, like that which is possessed by Neurotic medicines. And it is able to counteract a number of disorders, as Lepra and Impetigo, which are assumed to depend upon morbid actions in the blood. Arsenic has been recommended in Syphilis, but it exerts no marked power over that disorder. In ague it possesses this advantage over Quina, that it may be administered with safety during the paroxysm. The ordinary precautions in the administration of the Arsenical solution (Liquor Potassæ Arsenitis) have been already enumerated, viz., that the dose should be small at first, and afterwards gradually increased; that as soon as it produces swelling of the face and eyelids, or irritation of the stomach, it should be discontinued, or the dose reduced; and that it should generally be given on a full stomach, as it is then less likely to irritate. (_Vide_ pp. 140, 165, 170, 176, 207, 211, 213.) AMMONIA. Class I. Div. I. Ord. III. ALKALIA. Class II. Div. I. Ord. I. STIMULANTIA GENERALIA. Class IV. Ord. II. EXPECTORANTIA. Class IV. Ord. V. DIAPHORETICA. This medicine may be taken as the type of simple General Stimulants. It tends to excite the nervous forces generally. The remedies of this group are not very potent in their action, Ammonia being perhaps as powerful as any of them. Alcohol, an Inebriant Narcotic, produces at first a greater stimulant effect, but its action is followed up by a depression of the nervous forces, and an affection of the powers of the mind. This influence over the intellectual functions is confined to the Narcotic division of nerve-medicines, and is not possessed by Ammonia. Ammonia is capable of acting chemically as an alkali in the system, and may be used in the various cases in which alkalies are wont to be employed; but it is inferior to Potash in such disorders, because its affinities are far less powerful than those of that alkali. It is also caustic and irritant when applied externally in any form.