The use of tobacco in its relation to digestion is a subject very closely allied to dietetics, but a brief mention of it only can be made here. Like alcohol, undoubtedly most persons are better without it, and its abuse is well known to disorder digestion through the action of nicotine upon the circulation, and especially upon the vagus nerve. No definite rules can be formulated for the use of tobacco in relation to meals beyond those suggested by the fact that the action of tobacco is always less likely to prove irritating if it is smoked while there is abundant food in the stomach. The after-dinner cigar in many persons promotes the secretion of gastric juice, and there are those in whom a mild cigar after breakfast favours peristalsis and the evacuation of the bowels. If there is any tendency to indigestion of starchy or saccharine foods, it is usually aggravated by the use of tobacco in any form.

As observed elsewhere, when food cannot be obtained after fatiguing exercise or a forced march, the moderate use of tobacco is often found to temporarily replace it, at least to the extent of lessening the feeling of weariness. (See Substitutes for Food, p. 286.) Smoking immediately before meals may destroy the appetite and interfere with the digestion of the food.