ing in uneven teeth. The genus Nicotiana includes some fifty other species, mostly natives of America, but some of Australia and the islands of the Pacific Ocean. Of these, some fifteen or twenty species are cultivated and give rise to different foreign tobaccoes, the taste and properties of which are varied. A few species, remarkable for the richness of their colors and their graceful growth, are cultivated as ornamental plants in gardens.
Tobacco leaves contain principles common to all vegetable substances—such as starch, cellulose, sugar, organic acids, and salts principles soluble in ether, nitrogenous substances, and a peculiar alkaloid to which the plant owes its special qualities, called nicotine. This alkaloid, discovered by Posselt and Remann, was isolated by Vauquelin in 1809. It is an oily liquid, transparent and colorless, which becomes brown and thick in the air by absorbing oxygen. Its acrid and virulent odor is like that of tobacco; it has a burning taste, and its vapor is so irritating that breathing is painful in a room where a drop of it has fallen. It is very hygrometric, and soluble in water, alcohol, and ether. It combines directly with acids, with the evolution of heat. It is found as a malate in the leaves. The different kinds of tobacco do not contain the same quantities of it. The black, unctuous tobacco of the Antilles, the pronounced savor, ready burning, and white ash of which make it in demand among experienced smokers, contains much more nicotine than the light, fragrant tobacco of the Levant. The quantity of it increases with the development of the plant, and varies according to the thickness of the leaves. The thinner-leaved plants contain less of it. The fermentation to which tobacco is subjected in manufacturing volatilizes a part of the nicotine and substitutes ammonia for it. Consequently, there is less nicotine in tobacco prepared for consumption than there was in the dry leaves before the preparation. Combustion destroys about three quarters of this. According to M. Pabst, the smoke of five grammes of tobacco yields about three milligrammes of nicotine; but it contains a number of other principles besides, the enumeration of which here would not be interesting. Nicotine is the active principle of tobacco, as atropine is of belladonna and morphine of opium; but there are other poisons among the substances united with it. The less volatile ones condense during combustion, and produce a brownish empyreumatic liquid, a kind of coal-tar of tobacco, a part of which oozes through porous pipes, and the whole of which is retained in the water of nargilehs.
Among the volatile principles that pass into the smoke along with nicotine are hydrocyanic acid and carbonic oxide. Dr. Grehant has shown that a notable quantity of them is absorbed by rapid smokers swallowing the smoke, and the gas passes into the
