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 is ever to impair materially the energy of poisons, except in the instances of mercury, alcohol, and opium.

On the contrary, the tendency of habit when it does affect their energy, is, with a few exceptions, to lessen it. By the force of habit a person may take without immediate harm such enormous quantities of some poisons as would infallibly kill an unpractised person or himself when he began. There have been opium-eaters in this country who took for days together ten or even seventeen ounces of laudanum daily.

The influence of habit has been ascertained precisely in the case of a few common poisons only. On the whole, it would appear that more change is effected by habit in the action of the organic than in that of the inorganic poisons; and that of the former, those which act on the brain and nervous system, and produce narcotism, are altered in the most eminent degree. The best examples of the influence of habit are opium and vinous spirits. The action of such poisons is not always, however, entirely thrown away; they still produce some immediate effect; and farther, by being frequently taken, they may slowly bring on certain disease, or engender a predisposition to disease. A very singular exception to this rule prevails in the instance of tobacco; which, under the influence of habit, may be smoked daily to a considerable amount, and, so far as yet appears, without any cumulative effect on the constitution, like that of opium-eating or drinking spirits.

The inorganic poisons are most of them little impaired in activity by the force of habit. The pure irritants, indeed, do lose a little of their energy: for it seems that persons have acquired the power of swallowing with impunity considerable doses of the mineral acids. But as to inorganic poisons that enter the blood, habit certainly does not diminish, probably rather increases, their power. There is no satisfactory evidence, that a person by taking gradually-increasing doses of arsenic may acquire the power of enduring a considerably larger dose than when he began: On the contrary, the stomach rather becomes more tender to the subsequent dose by each repetition. I have little hesitation in avowing my disbelief of the alleged cases of arsenic-eaters and corrosive-sublimate-eaters, who could swallow whole drachms at once with impunity. Some have expressed surprise at this statement having been made in former editions of the present work, when there is such authority as Byron, Pouqueville, &c., for the hacknied story of Soleyman, the sublimate-eater of Constantinople, who lived to the age of a hundred, eating a drachm of corrosive sublimate daily. I must avow, however, that such reporters of a feat so very extraordinary, and where deception was so highly probable, are to me no authority at all.

In the relative influence of habit on poisons of the three kingdoms of nature, a new argument will be discovered for the opinion given above respecting the partial decomposition of organic poisons in some of the tissues. In fact this partial decomposition accounts very well for the effect of habit: The effect of habit is probably nothing more than an increased power acquired by the stomach of decomposing the