We may see, by this example, how much room is always left for fallacy in the empirical tracing of physiological effects to their causes. The phænomena are so complex that induction is of but little avail, unless supported and confirmed by deduction.[25] In the case of tobacco, our conclusions are so confirmed. Deduction, supported by cautious induction, shows the stimulant action of tobacco to be of permanent benefit to the system; and hence the statements of those smokers who believe themselves injured by the habit must be received with due qualifications. Yielding unsuspiciously to the influence of a prejudice which originated in an absurd puritanical notion of "morality,"[26] many smokers are in the habit of reviling the practice which they nevertheless will not abandon. Having once begun to smoke, they persist in laying to the account of tobacco sundry aches and ails which in the hurry and turmoil of modern life no one can expect wholly to escape, and many of which are such as tobacco could not possibly give rise to. If their teeth, for instance, begin to decay, tobacco gets the blame, although it is notorious to dentists that tobacco preserves the enamel of the teeth as hardly anything else will. We have seen teeth which had been kept for months in a preparation of nicotine and were in excellent condition. Then the headache, due perhaps to an overdose of hot risen biscuit or viands cooked in pork-fat, is quite likely to be laid to the charge of the general scape-goat; although to produce a headache directly by means of tobacco requires a powerful narcotic dose.[27] One of the chief causes of ordinary headache is doubtless the use of the execrable anthracite which Pennsylvania protectionists force upon us by means of their unrighteous prohibitory tariff upon English coal.[28] We have even heard it alleged that smoking impairs the eyesight. Students smoke much, and are nearsighted, is the complacent argument--it being apparently forgotten that sailors smoke much and are far-sighted, and that in each case the result is due to the way in which the eyes are used. [25] Mill's _System of Logic_, 6th ed. vol. I. pp. 503-508. [26] "The Puritans, from the earliest days of their 'plantation' among us, abhorred the fume of the pipe." Fairholt, _Tobacco, its History, etc._, p. 111. [27] Smoking has also been charged with acting as a predisposing, or even as an exciting, cause of insanity,--a notion effectually disposed of by Dr. Bucknill, in the _Lancet_, Feb. 28th, 1857.