Closely related to the cause, are the circumstances under which disease, and the conditions which modify it, makes its appearance. These are commonly known as the modalities; they individualize and define every sickness as well as every drug, hence the most suitable medicine cannot be chosen while they remain unknown. They include such modifying agents as the effect of posture; the different kinds of motion, the various forms of heat and cold, the effects of the weather, or bathing, washing, getting wet or any modifying agent whatsoever.
Many odd or strange modifying influences also occur; they belong to but few remedies and are not often seen in practice, but possess the highest value. A striking instance of this kind is found under Clematis which has an eczema which is moist during the increasing moon but dries up during the waning moon. We now known that his modality belongs almost exclusively to Clematis and that any symtoms having it will almost certainly belong to this great antisycotic, whether it be a skin eruption or a goitre.
Conditions which modify or excite mental symptoms are not exceeded in importance by any others. To these belong the influence of the emotions, of fright, grief, solitude or company, thinking of the disease, consolation, vexation, etc., on the mind. “Pain which excites to anger” is an excellent example.