To how many substances this power of accumulation extends is at present not well understood. It may occur in those that act by absorption, and in those whose action is wholly local. Arsenic, digitalis, and several of the narcotic plants, as hemlock, may undoubtedly occasion serious mischief in this manner, as the author has more fully explained in another work,[150] and we have lately heard of several fatal cases arising from accumulated masses of magnesia in the _primæ viæ_, from the habitual use of small doses of that earth. The history of many of the arts, especially those of metallurgy, would furnish also abundant examples of this kind of poisoning. These few facts are we trust sufficient to authorise the foregoing arrangement, and we apprehend that the adoption of the distinctions, upon which it is founded, will be of great service in establishing fixed and definite notions with regard to the _chronic_ operation of poisons. It may perhaps be useful to present the reader with a synoptical recapitulation of the subject. _A Slow Poison._ A single dose is sufficient; which produces upon its administration no sensible effect, but gradually undermines the health. _A Consecutive Poison._ A single dose is sufficient; producing the most violent symptoms, very shortly after its ingestion, but which gradually subside, and the patient is supposed cured; when, at some future period, death takes place from the organic lesions that had been occasioned. _An Accumulative Poison._ Many doses are required; the effects being produced by the repetition of doses which would, _individually_, be harmless.