Tobacco contains and depends largely for its effects upon considerable amounts of a substance called _nicotine_.
This is a powerful poison, even in very small doses, with only feeble narcotic, or pain-deadening, powers; but fortunately, the larger part of it is destroyed in the process of burning.

Enough, however, is carried over in the smoke, or absorbed through the butt of the cigar or cigarette, or the mouth-piece of the pipe, to injure the nervous system, especially in youth.

As will be seen in the chapter upon the "Care of the Heart," it especially attacks the nerves supplying the heart, and is thus most harmful to growing boys.
On account of its injurious effects upon the nerves of the heart, smoking has long been forbidden by trainers and coachers to all athletes who are training for a contest or race.

In addition to its poisonous effects upon the nervous system, tobacco also does great harm to boys and young men by providing them with an attractive means of filling up their time and keeping themselves amused without either bodily or mental effort.

The boy who smokes habitually will find it much easier to waste his time in day-dreams and gossip, and tends to become a loafer and an idler.
The Advantage that Non-Smokers have over Smokers.