This definition has no reference to the time or the quantity required to produce the effect. There is a wide difference in both these respects between different poisons. Some are slow, and some rapid in their operation. Some, as for example opium, arsenic, and prussic acid, act as poisons in small amounts; while comparatively large quantities of such articles as lobelia, saltpetre, and salæratus, are required to produce ‘deleterious,’ and especially ‘fatal’ effects; and yet lobelia, saltpetre and salæratus are as truly poisons as are opium, arsenic and prussic acid. It may be remarked also that this definition has reference only to the _usual_ effects of substances; and not to any occasional effects which may be owing to circumstances. If, for example, any substance produce a bad effect simply from the influence of any constitutional peculiarity, or some temporary condition of the system, it is not to be called a poison. The term poison is used often in relation to the effects of substances in such cases, but it is only in a _relative_ sense. Anything may be a poison in this sense. Anything which is inappropriate to any case will produce a ‘deleterious’ influence upon it, and is therefore a poison to it. Food may thus be for the time being a poison to the sick man, as really as a noxious drug. Indeed a noxious drug may be to him a cure, while in the same quantity it would be perhaps even a fatal poison to him if he were well. Thus a man sick with spasmodic colic is relieved by opium, which is a noxious drug to a well man; and perhaps, in order to produce the relief, he requires as much as would kill him if he were in a state of health. The word poison carries terror to most minds, and it has therefore been one of the watchwords of Thompsonians and other quacks, in their warfare upon the medical profession. And yet, while they are raising this ridiculous outcry, they themselves, as I have before said, daily use poisons, even mineral poisons, as common articles of food. Salæratus, cream of tartar, and even common salt,[13] are poisons, for when taken in large quantities, they prove ‘deleterious,’ in some cases ‘fatal,’ and therefore come within the terms of the definition. I have said thus much of the popular prejudice on the subject of poisons, and the use which Thompsonians and other quacks have made of it, because there is so general a misapprehension in regard to these points abroad in the community. I cannot conclude this chapter without noticing the changes which have taken place in the sentiments and practice of Thompsonians within the last few years. These changes have been quite material. I have already alluded to some of them.