The dried leaves of Virginian Tobacco,

Nicotiana Tabacum. Cultivated in America.

Characters. - Large, mottled-brown, ovate or lanceolate, acuminate leaves, up to twenty inches (50 centimetres) long, bearing numerous short, glandular hairs; having a peculiar, heavy odour and nauseous bitter, acrid taste; yielding, when distilled with solution of potash, an alkaline fluid, which has the peculiar odour of nicotine, and precipitates with perchloride of platinum and tincture of galls. Not manufactured.

Composition.- A volatile liquid alkaloid, nicotine, is contained in tobacco as a malate, and is obtained by distillation with an alkali. The leaves contain also nicotianin, or tobacco-camphor, which crystallises out from an aqueous distillate. Resin, gum, and several inorganic compounds are also present.

General Action. - Tobacco stimulates and then paralyses the motor nerves of involuntary muscles and the secreting nerves of glands. In consequence of this action on the gastrointestinal tract, there is in poisoning by tobacco nausea and vomiting, with intense prostration and wretchedness. In consequence of the action of the drug on the heart and vaso-motor system, there is paleness of the face, cold sweats, feebleness of circulation, and tendency to faint. The action of tobacco is the same as that of its alkaloid, nicotine, though less powerful. In frogs, nicotine, after a period of temporary excitement, causes a tetanic condition in a peculiar attitude, the head being drawn down, the fore legs back, and the hind legs forward; there may be convulsions. This is followed by muscular relaxation. In warm-blooded animals there is excitement, difficulty of breathing, followed by trembling, with expulsion of urine and faeces, stupor, staggering gait, convulsions, and death. When the dose is very large, the animal may fall with a loud cry and the convulsions begin at once, deepening into muscular paralysis; and death ensues from failure of respiration, the heart continuing to beat after respiration ceases.

Special Action. - The spinal cord is first stimulated (p. 181), giving rise to convulsions, and is afterwards paralysed. The convulsions are of spinal origin in the frog, as is shown by such experiments as have been already mentioned (p. 180), but those which occur before death in mammals are probably asphyxial.

Circulation. - Nicotine causes a great diminution of pulse-rate and a fall, followed by a rise, of blood-pressure, the pulse-rate still remaining slow; but if a large dose be given, the pulse-rate rises very quickly. The drug first stimulates both the vagus roots and its ends in the heart (causing slow pulse-rate), and then paralyses the latter (causing high pulse-rate). It does not, however, paralyse the inhibitory ganglia of the heart, like atropine, since stimulation of the sinus will slow the heart in frogs after nicotine-poisoning. The primary fall of blood-pressure is due to the slowing of the heart, and the subsequent rise to contraction of the peripheral vessels.

Alimentary canal. - Nicotine stimulates peristalsis markedly (p. 383).

The methyl and ethyl derivatives of nicotine have no teta-nising influence on the cord, neither, curiously enough, do they paralyse the ends of the motor nerves.

Uses. - Tobacco is used as an enema in supposed intussusception, and was formerly used in the reduction of strangulated hernia, but as death has occurred from this treatment it must be employed with care.

Owing to its influence on the cord, nicotine has been used in tetanus and strychnine-poisoning, but is not of much use.

Tobacco-smoking. - The effects produced on the system by tobacco-smoking may be partly due to nicotine, but are probably rather due to products of its decomposition such as pyridine and collidine. In pipe-smoking pyridine (p. 810) preponderates, but when tobacco is smoked in cigars, where there is free access of air, the chief product of the dry distillation undergone by the tobacco is collidine, which is far less active than pyridine (Vohl and Eulenburg, vide p. 812).

In those accustomed to smoke tobacco, it has a soothing effect on the nervous system, but it often acts as a nervous stimulant to mental work, as in reading. In these cases the effect is probably not due to the nicotine itself, but to the stimulus of the smoke on the sensory nerves of the mouth, which reflexly stimulates the vaso-motor centre, and dilates the vessels of the brain; since some people produce the same effect by sucking sweets, or sipping whisky and water (p. 193).

There is no doubt that smoking in excess is injurious. It produces a furred tongue, irritation of the throat, hoarseness, often dyspepsia and irritability of the heart, with a characteristic rhythm and palpitation (smoker's heart). This effect on the heart is like that produced by partial paralysis of the vagus, and disappears when the habit is given up for a time.

Sudden faintness is also apt to occur, so that a previously strong and healthy man will suddenly fall down in a state of syncope without apparent cause, or the faint may be brought on by some mental emotion.

The sight is impaired by habitual excess in tobacco-smoking (p. 228).

Tobacco-smoking is often very useful in asthma, and a pipe after breakfast will often relieve constipation.

Tobacco-snuff is used as an errhine.