The operation of medicines is influenced by certain general circumstances, which should be also kept in mind when we apportion their dose; e.g. AGE—SEX—TEMPERAMENT—STRENGTH OF THE PATIENT—HABIT—DIET—PROFESSION—CLIMATE—DURATION OF THE DISEASE—STATE OF THE STOMACH—IDIOSYNCRASY—and THE VARIABLE ACTIVITY OF THE MEDICINAL SUBSTANCE. Women generally require smaller doses than men. Habit, or the protracted use of a medicine, generally diminishes its power, although certain cathartics appear to offer an exception, for when long continued, their activity is proportionally increased, as is well known to every person who is familiar with the operation of the Cheltenham waters. Dr. Lamb has also stated with regard to the operation of Lead, “that the constitution, so far from being reconciled to it by habit, is rendered more and more sensible to its irritation by continuance.” Emetics also frequently become more powerful by repetition; Cullen informs us that he knew a person so accustomed to excite vomiting in himself that the one twentieth part of a grain of tartarized antimony was sufficient to excite a convulsive action of the stomach; in some cases such an effect may perhaps be referred to the operation of the mind; for after the frequent use of an emetic, the mere sight of it, or even conversation relative to it, has been found sufficient to excite nausea. In apportioning the dose of a very active medicine, it is of the greatest moment to determine the relative degrees of power between the system and the remedy, and to know to what extent the latter is likely to be carried, consonantly with the powers of life to resist it; thus, after a patient has been exhausted by protracted and severe suffering and watching, a dose, different to one at the commencement of the disease is requisite. The importance of this precept is impressed upon my mind from having witnessed, in the course of my practice, several instances of the mischief which has arisen from a want of attention to it; that disease materially influences the condition of the body, and its susceptibility to remedial impressions, has been already demonstrated. Emetics act very readily in febrile affections, while in those of the Neuroses[286] they produce their effects with difficulty. In the application of external remedies to diseased parts, it especially behoves the Surgeon to take into consideration the degree of vitality possessed by such parts, and to graduate their strength accordingly.