The active principle of tobacco is nicotine, besides which it contains an aromatic camphor-like substance, cellulose, resins, sugar, etc. Other products developed during combustion are carbon monoxide gas, a minute amount of prussic acid and in some varieties a considerable amount of furfural, a poison. From any one cigar or cigarette but little nicotine is absorbed, else the user would be poisoned.

The most important action of nicotine is on the circulation. The heart is frequently made more rapid and the blood pressure is certainly raised in an ordinary smoker, while even a novice may get at first an increase, but soon he may become depressed and have a lowering of the pressure. While a moderate smoker may have an increase of 10 mm. in blood pressure, an excessive smoker may show but little change. Perhaps this is because his heart muscle has become weakened. If the person's blood pressure is high, the heart may not increase in rapidity during smoking, and if he is nervous beforehand and is calmed by his tobacco, the pulse will be slowed. It has been shown that the blood pressure and pulse rate may be affected in persons sitting in a smoke-filled room, even though they themselves do not smoke. The length of time the increased pressure continues depends on the person, and it is this diminishing pressure that causes many to take another smoke. The heart is slowed by the action of nicotine on the vagi, as these nerves are stimulated both centrally and peripherally. An overdose of nicotine will paralyze the vagi. The heart action then becomes rapid and perhaps irregular. The heart muscle is first stimulated, and if too large a dose is taken, or too much in twenty-four hours, the muscle becomes depressed and perhaps debilitated. The consequence of such action on the heart muscle, sooner or later, is a dilation of the left ventricle if the overuse of the tobacco is continued.

In a word, the heart muscle is always weakened by excessive indulgence in nicotine, the nerves of the heart is disturbed, if not actually injured. Therefore everyone who smokes should quit it.

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