Now to say that a substance is a poison is not to say that it inevitably kills; it may be apparently innocuous, if not incidentally beneficial. King Mithridates, it is said, learned habitually to consume these dangerous commodities; and the scarcely less mythical Du Chaillu, after the fatigues of his gorilla warfare, found decided benefit from two ounces of arsenic. But to say that a substance is a poison is to say at least that it is a noxious drug,--that it is a medicine, not an aliment,--that its effects are pathological, not physiological,--and that its use should therefore be exceptional, not habitual. Not tending to the preservation of a normal state, but at best to the correction of some abnormal one, its whole value, if it have any, lies in the rarity of its application. To apply a powerful drug at a certain hour every day is like a schoolmaster's whipping his pupil at a certain hour every day: the victim may become inured, but undoubtedly the specific value of the remedy must vanish with the repetition. Thus much would be true, were it proved that tobacco is in some cases apparently beneficial. No drug is beneficial, when constantly employed. But, furthermore, if not beneficial, it then is injurious. As Dr. Holmes has so forcibly expounded, every medicine is in itself hurtful. All noxious agents, according to him, cost a patient, on an average, five per cent. of his vital power; that is, twenty times as much would kill him. It is believed that they are sometimes indirectly useful; it is known that they are always directly hurtful. That is, I have a neighbor on one side who takes tobacco to cure his dyspepsia, and a neighbor on the other side who takes blue pill for his infirmities generally. The profit of the operation may be sure or doubtful; the outlay is certain, and to be deducted in any event. I have no doubt, my dear Madam, that your interesting son has learned to smoke, as he states, in order to check that very distressing toothache which so hindered his studies; but I sincerely think it would be better to have the affliction removed by a dentist at a cost of fifty cents than by a drug at an expense of five per cent. of vital power.