[Illustration: FIG. 36. Effect of cigarette smoking.] [Sidenote: Proof that tobacco is a poison] Tobacco is a poison. Those of you who have tried to smoke know this, because it made you sick the first time you tried it. There are many other indications that tobacco is a poison. We know that it affects the red blood cells in such a way that they do not carry the oxygen as well as do those of people who do not smoke. We know that it has a very bad effect on the heart and that it interferes with the action of the nervous system. [Sidenote: The extra work caused by tobacco] When certain poisons get into the body, the blood makes something that will counteract the effects of those poisons. After one has used tobacco for some time, the cells of the body will take care of the tobacco poison by making an antidote for it. More than this, they begin to want it all the time. The tobacco user forces the cells of his body to make an antidote for this poison every time he uses tobacco. Thus he makes the cells do work that is unnecessary, and keeps them from doing work that is necessary. [Sidenote: Other bad effects of tobacco: (_1_) On the nose and throat] Tobacco smoke irritates the cells that line the throat and nose and causes inflammation. This is why so many smokers have catarrh. Smoking is not the only cause of catarrh, for people who do not smoke often have this trouble, but it is one of the most frequent causes. Smoking also irritates the throat so badly that many of those who smoke have "smoker's throat." This is a bad form of sore throat that can be cured only by stopping the use of tobacco. [Illustration: FIG. 37. The athlete knows that alcohol and tobacco are foes to speed, strength, and nervous control. (_From photograph of "The Sprinter," modelled by Dr. R. Tait McKenzie._)] [Sidenote: (_2_) On the blood] People who smoke a great deal have fewer red corpuscles (the little red cells of the blood) than those who do not smoke. Especially is this true of cigarette smokers. It is the lack of red blood cells that causes the cigarette smoker to look pale and sallow. It is probably not the direct effect of tobacco that causes the loss of red blood cells, but something that is connected with the act of smoking. When you take smoke into your mouth, you take in at the same time a gas known as _carbon monoxid_. This gas is very poisonous to the body, and combines with the red blood cells in such a way that they cannot take up the oxygen in the lungs and carry it to the rest of the cells in the body. The cigarette smoker almost always inhales the smoke, and thus he absorbs a great deal more of the carbon monoxid than the man who does not inhale the smoke. Of course, the more of this gas he takes into his body, the more red blood cells will be affected and the less oxygen will be taken to the other cells. [Sidenote: (_3_) On the nervous system]