Few persons who have not been specially educated in science have ever learned this great lesson of Materia Medica, "that everything depends on the size of the dose." It is not merely that a small dose will often produce effects differing in degree from those produced by a large dose; nor is it merely that the small dose will often produce an effect differing in kind from that of the large dose; but it is that the small dose will often produce effects diametrically opposite and antagonistic to those of the large dose. The small dose may even serve as a partial antidote to the large dose. The adage concerning the hair of the dog that has bitten us, embodies the empirical wisdom of our ancestors on this subject. Especially is this true of all the substances classed as narcotics. In doses of a certain size, they, one and all, produce effects exactly the reverse of narcotic. If anything is entitled to be called a deadly narcotic poison, it is strychnia, which, by paralyzing the spinal cord, induces tetanic convulsions: yet minute doses of strychnia have been used with signal success in the cure of hemiplegic paralysis. In teething children, the pressure upon the dental branches of the trigeminal nerve sometimes causes an irritation so great as partly to paralyze the medulla, inducing clonic convulsions, and perhaps death by interference with the heart's action.[7] In these cases, alcohol has been frequently used with notable efficacy, averting as it does the paralysis of the medulla. Epileptic fits, choreic convulsions, and muscular spasms--such as colic, and spasmodic asthma--are also often relieved by the tonic or anti-paralytic action of alcohol. And how often has the temperate smoker, after some occasion of distressing excitement, his limbs and viscera trembling, his nerves "all unstrung," or incipiently paralyzed,--how often has the temperate smoker found his whole system soothed and quieted, and the steadiness of his nerves restored, by a single pipe of tobacco! That this is due to its action as a counteracter of paralysis is shown by the fact that tobacco has been successfully used in tetanus,[8] in spasm of _rima glottidis_,[9] in spasmodic asthma,[10] and in epilepsy.[11] For these phenomena physiology has but one explanation. They are due to the fact that narcotics, in small doses, either nourish, or facilitate the normal nutrition of the nervous system. They restore its equilibrium, enabling it, with diminished effort, to discharge its natural functions. And anything which performs this office is, in modern physiology, called a _stimulant_. [7] Clendon, _On the Causes of the Evils of Infant Dentition_. [8] Curling, _On Tetanus_, p. 168; Earle, in _Med. Chir. Trans._, vol. vi., p. 92; and O'Beirne, in _Dublin Hospital Reports_, vols. i. and ii. [9] Wood, _U.S. Dispensatory_. [10] Sigmond, in _Lancet_, vol. ii., p. 253.