Tobacco is the leaves of Nicotiana tabacum (Fam. Solanaceae), subjected to a process of fermentation to remove certain proteins and fats that would make the smoke disagreeable, and then to another process of fermentation by which 25 or 30 per cent. of the nicotine is lost and the aroma developed. The chief constituents of the cured leaves (not the smoke) are the volatile liquid alkaloid, nicotine, some related alkaloids, and a volatile oil to which most of the aroma is due. (For the constituents of the smoke see below.) The Havana tobacco is noted for its delicate aroma, and usually contains only 1 to 3 per cent. of nicotine; while some of the Virginia and French tobaccos may yield as much as 6 or 7 per cent. An examination of Virginia tobaccos by the Virginia Agricultural Experiment Station in 1898 showed 1.68 to 6.17 per cent. of nicotine. Turkish tobacco comes from Nicotiana Rustica, and contains about 2.5 per cent. of nicotine (Kew Bulletin).

The cured tobacco is used for smoking; or, mixed with molasses, extract of licorice, and other flavoring materials, is used for chewing (chewing-tobacco). When powdered, also sometimes scented and flavored, it constitutes snuff, which is used by snuffing into the nose or rubbing upon the gums.

For smoking, tobacco is burned in a pipe, or in the form of cigarrete or cigar, the smoke being drawn through the tobacco into the mouth, or sometimes "inhaled," that is, drawn into the lungs. A method of drawing the smoke through water or rose-water, as in the "hookah," is in vogue in eastern countries. It is said that this takes out about half the poison and cools the smoke. The smoke contains nicotine, pyridine, quinoline, hydrocyanic acid, irritant aldehyds, ammonia, furfurol, phenols, carbon dioxide, carbon monoxide, and some volatile oil. How much of the nicotine of tobacco is destroyed in the smoking is a question. Allen says that "the greater part of the nicotine is converted into pyridine and other pyrogenous compounds," and Bush, and Vohl and Eulenberg found no nicotine at all in the smoke. As pyridine is only one-twentieth as poisonous as nicotine this would explain the absence of serious acute symptoms from smoking. Other investigators, however, report the recovery from the smoke of one- to four-fifths of nicotine. Lehmann (1912) has shown that the hydrocyanic acid is not a factor in the tobacco effects; but the investigations of the London Lancet (1912) point to furfurol aldehyd and other aldehyds as harmful constituents. Furfurol is a constituent of the fusel oil of alcohol, and the Lancet experiments show that a single cigarette may contain as much of it as two ounces of whisky. Furfurol, of which a dose of 1 1/2 grain (0.1 gm.) is capable of producing a persistent headache, is practically absent from the smoke of Turkish cigarettes.

In medicine, tobacco has been employed externally in the form of a poultice, and internally as an emetic, and the smoke has been inhaled in spasmodic asthma; but, owing to its great toxicity and to the great difference in human susceptibility to its action, it is dangerous as a remedy and has been omitted from the Pharmacopoeia. Tobacco is still used more or less in asthma, and in addition to stramonium, lobelia, or cubebs, forms a constituent of many of the asthma cigarettes and cigars. As its value is so limited, tobacco is to be considered chiefly because of the effects of the tobacco habit.

The world's output has been placed at 2,000,000,000 pounds a year. In the United States alone in 1913, according to the internal revenue reports, the output of manufactured tobacco was 410,976,513 pounds, while the cigarettes numbered over 15,000,000,000 and the cigars over 8,500,000,000. That would be over 4 pounds of tobacco and over 85 cigars and 150 cigarettes for each inhabitant. In addition, 33,000,000 pounds of snuff were manufactured.

Pharmacologic Action Of Nicotine

Nicotine is rapidly absorbed from skin and mucous membranes. Its main action is a brief stimulation of the cerebrum, medulla, and cord, of the ganglia on the vagus and sympathetic nerves, and of the motor end-plates in voluntary muscle, the stimulation being followed by depression.

Alimentary Tract

The saliva is increased and there may be biting of the tongue from the irritant nicotine. Either from the local effect of the swallowed saliva or from its systemic effect after absorption there may be nausea, vomiting, and increased peristalsis with diarrhea.

Circulation

The stimulation of the vagus center and ganglia results in a slowing of the heart, and that of the vasoconstrictor centers and ganglia in a great rise in blood-pressure; the subsequent depression shows in a rapid heart and lowered blood-pressure. From smoking, a preliminary rise is not uncommon during the first fifteen or twenty minutes, but it may be absent in those who are very tolerant of the drug. To one who is not habituated the subsequent fall in pressure may result in mild collapse. A fall of 50 mm. has been noted. Cannon, Aub, and Binger (1912) have shown that nicotine can cause increased activity of the adrenals.

Respiratory

This center is also stimulated, then depressed. The bronchial muscles, from stimulation followed by depression of the ganglia of the motor nerves, undergo a transient contraction, followed by persistent relaxation; hence the use of tobacco in spasmodic asthma.

Smooth muscle of all kinds is affected through the ganglia of the supplying nerves.

The pupil is contracted at first and subsequently dilated. This is from an effect on the third-nerve ganglia.

The cerebrum is only slightly stimulated, and this effect so quickly passes into depression that the drug is a true narcotic or cerebral sedative. Tobacco is not an intellectual stimulant, but just the reverse.

The medullary centers and the reflexes are at first stimulated, then depressed.

Toxicology

The poisonous effects of tobacco (not tobacco smoke) are due chiefly to nicotine. Two drops of nicotine placed on the tongue or rubbed into the gums of a small dog or cat will produce death in one or two minutes. A large mastiff died almost instantly when ten drops were placed on his tongue, and a canary when one drop was held near its bill. In man death has followed the use of tobacco as a poultice, the application of an infusion in skin disease, the injection of an infusion into the rectum for worms, the plugging of a wound with a quid of tobacco to stop the bleeding. etc. In fact, a cigar may contain enough nicotine to kill two unhabituated adults. Fortunately in smoking the nicotine is changed, at least to a considerable degree, and much of that present is exhaled and lost.