Tobacco contains a powerful narcotic poison, nicotin, which resembles prussic acid in the rapidity of its action, when a fatal dose is taken.
"How to Live" by Irving Fisher and Eugene Fisk
Chemically it is methyl-tetrahydro-nicotinic acid.
"Encyclopaedia Britannica, 11th Edition, Volume 3, Slice 6" by Various
Nicotine is nearly as powerful and rapid as prussic acid with the animal economy.
"The International Monthly, Volume 4, No. 1, August, 1851" by Various
The substances which differentiate tobacco from other plants and form its chief characteristics are Nicotianin, Nicotine and Malic Acid.
"Tobacco Leaves" by W. A. Brennan