These narcotics are Opium, Hemp, the Betel, Coca, Thorn-Apple, Siberian Fungus, Hops, Lettuce, Tobacco.  The active principles vary in each, thus differing from foods and stimulants.  Our business is now to inquire into the chemical constituents of tobacco.

The leaves of this plant owe their properties to certain invariable active principles, which chemistry has enabled us to separate from those ingredients which are either inert or common to it and other forms of vegetation.  They are two in number,—­a volatile alkali, and a volatile oil, called nicotin and nicotianin, respectively.  A third powerful constituent is developed by combustion, which is named the empyreumatic oil.

Starch, gum, albumen, resin, lignin, extractive, and organic acids exist in tobacco, as they do, in varying proportions, in other plants.  But the herb under consideration contains a relatively larger proportion of inorganic salts, as those of lime, potassa, and ammonia,—­and especially of highly nitrogenized substances; which explains why tobacco is so exhausting a crop to the soil, and why ashes are among its best fertilizers.

The organic base, nicotin, (or nicotia, as some chemists prefer to call it,) exists in tobacco combined with an acid in excess, and in this state is not volatile.  As obtained by distillation with caustic soda, and afterwards treated with sulphuric acid, etc., it is a colorless fluid, volatilizable, inflammable, of little smell when cold, but of an exceedingly acrid, burning taste, and alkaline.  Nicotia contains a much larger proportion of nitrogen than most of the other organic alkalies.  In its action on the animal system it is one of the most virulent poisons known.  It exists in varying, though small proportion, in all species of tobacco.  Those called mild, and most esteemed, seem to contain the least.  Thus, according to Orfila, Havana tobacco yields two per cent of the alkaloid, and Virginia nearly seven per cent.  In the rankest varieties it rarely exceeds eight parts to the hundred.  The same toxicologist says that it has the remarkable property of resisting decomposition in the decaying tissues of the body, and he detected it in the bodies of animals destroyed by it, several months after their death.  In this particular it resembles arsenic.

Nicotianin, or the volatile oil, is probably the odorous principle of tobacco.  According to some, it does not exist in the fresh leaves, but is generated in the drying process.  When obtained by distillation, a pound of leaves will yield only two grains; it is therefore in a much smaller proportion than the alkaloid, forming only one half of one per cent.  It is a fatty substance, having the odor of tobacco-smoke, and a bitter taste.  Applied to the nose, it occasions sneezing, and taken internally, giddiness and nausea.  It is therefore one of the active constituents of tobacco, though to a much less degree than nicotin itself.  For while Hermstadt swallowed a grain of nicotianin with impunity, the vapor of pure nicotin is so irritating that it is difficult to breathe in a room in which a single drop has been evaporated.