Alteratives, a term applied by modern writers on medical science in a somewhat obscure manner. A certain class of substances are denominated "alteratives" in manuals of therapeutics. The effects produced by these substances, administered in comparatively small and frequent doses, are practically known, but the modus operandi is a mystery. As the same substances in large doses act as emetics, purgatives, or poisons, a name was required to designate the peculiar effects of these substances administered in minute doses; and the most appropriate word that could be found, apparently, was the word " alterative." As the manner of action of drugs in health and disease becomes more accurately known, the medicines thus designated will undoubtedly be removed to other classes, or this name will be replaced by something more rational and definite. It is probable that some alteratives act either by modifying the character of the nutritive material carried by the blood to the tissues, or by promoting the destructive metamorphosis of tissue outside the blood vessels. In these processes, diseased tissues, being the more weakly organized, experience the earliest effects, and in this way the good may be obtained without the evil.

The principal substances used as alteratives are iodine and mercury, and their respective combinations with potassium and other substances. Arsenical preparations are also used as alteratives in small doses. They are mostly employed in chronic diseases and cutaneous, scrofulous, and syphilitic affections. Many other substances are now used as alteratives in small doses, the effects being more or less immediate and temporary, or slow and lasting, according to the dose administered. Any powerful medicine given in frequent small doses may be called an alterative, therefore, as it acts continuously, gently, slowly, and, when well selected, often most efficiently. Each medicinal substance acts in proportion to the frequency and potency of the dose administered, when given alone, or with a neutral menstruum, such as mucilage or water. Ten grains of ipecacuanha, taken alone or in water, act as an emetic; but combined with a strong dose of opium (two grains of good quality, or three of an inferior kind), the ipecacuanha will not produce an obvious effect upon the stomach, but be absorbed into the blood and cause a profuse flow of perspiration, if the patient be kept warm in bed. Arsenic is a violent poison in large doses; in minute doses, frequently repeated, it is a cure for ague and fever.

Many of the most active and poisonous preparations of mercury are highly beneficial in small doses, although dangerous in large ones.