We are, however, very ignorant of the effect of small, continued doses of the various tobacco poisons. All drugs comparatively harmless, such as lead, mercury, and arsenic, produce a highly injurious effect when taken in repeated small doses. Just what effect the use of tobacco engenders we cannot absolutely know, but no physician doubts that smoking may be a factor in almost any disease from which his patient is suffering. There can be, for instance, no question that smoke simply as smoke irritates the mucous membrane of the bronchial tubes and renders them more susceptible to infections; by irritating the mucous membrane of the nose and throat it tends to produce catarrh and therefore catarrhal deafness. It would therefore seem fair to state that the man who does not use tobacco is less susceptible to disease and contagion, and recovers more quickly from a serious illness or operation. From this we should expect to find that tobacco shows most in later life, when vitality is ebbing and the machinery of the body is beginning to wear. It is in his middle age that a man begins to feel the harm. In short, though we know only the precise or immediate effect of nicotine and only _some_ of the _morbid processes_ which excessive smoking may produce, it is likely that the worst aspect of tobacco is something that we do not know very much about--its tendency to reduce a man's general vigor. The dominant characteristic of tobacco is the fact that it heightens blood-pressure. The irritant action by which it does this sometimes leads to still more harmful results. Its second action is narcotic: it lessens the connection between nerve-centers and the outside world. These two actions account for all the good and all the bad effects of tobacco. As a narcotic, it temporarily abolishes anxiety and discomfort by making the smoker care less about what is happening to him. But it is a well-known law of medicine that all the drugs which in the beginning lessen nerve-action increase it in the end. Thus smoking finally causes apprehension, hyper-excitability, and muscular unrest. Here this inevitable law seems to give contradictory results. Every physician knows that an enormous amount of insomnia is relieved by smoking, even if it is at the expense of laziness the next day; at the same time every physician knows that most excessive smokers are troubled with insomnia. CIGARETTES