no one who has tried to eat unmoistened food, when thirsty, will dispute its uses as a solvent. tobacco seems to be a direct stimulant to the salivary apparatus. habit blunts this effect only to a limited extent. the old smoker has usually some increase of this secretion, although he does not expectorate. but if he does not waste this product, he swallows it, it is said, in a state unfit to promote digestion. the saliva owes its peculiarity to one of its components, called _ptyalin_. and this element possesses the remarkable power of converting starch into sugar, which is the first step in its digestion. though many azotized substances in a state of decomposition exert a similar agency, yet it is possessed by _ptyalin_ in a much greater degree. the gastric juice has probably no action on farinaceous substances. and it has been proved by experiments, that food moistened with water digests more slowly than when mixed with the saliva. more than this, the conversion of starch into sugar has been shown to be positively retarded in the stomach by the acidity of the gastric secretions. only after the azotized food has been somewhat disintegrated by the action of the gastric juice, and the fluids again rendered alkaline by the presence of saliva, swallowed in small quantities for a considerable time after eating, does the saccharifying process go on with normal rapidity and vigor. now starch is the great element, in all farinaceous articles, which is adapted to supply us with calorifacient food. in its original condition, either raw or when broken up by boiling, it does not appear that starch is capable of being absorbed by the alimentary canal. by its conversion into sugar it can alone become a useful aliment. this is effected almost instantaneously by the saliva in the mouth, and at a slower rate in the stomach. obviously, then, if the use of tobacco interferes with the normal action of the saliva, and if the digestion of starch ends in the stomach, here is the strong point in the argument of the opponents of tobacco. we should wonder at the discrepancy between physiology and facts, theory and the evidence of our senses and daily experience among the world of smokers, and be ready to renounce either science or the weed. fortunately for our peace of mind and for our respect for physiology, the first point of the proposition is not satisfactorily proved, and the second is untrue. we are not certain that nicotin ruins ptyalin; we are certain that the functions of other organs are vicarious of those of the salivary glands. we say that it is not satisfactorily proved that tobacco impairs the sugar-making function of the saliva. at least, we have never seen the proof from recorded experiments. such may exist, but we have met only with loose assertions to this effect, of a similar nature to those hygienic _dicta_ which we find bandied about in the would-be-physiological popular journals, which are so plentiful in this country, and which may be styled the yellow-cover literature of science. we acknowledge this to be the weak point in our armor, and are open to further light. yet more, for the sake of hypothesis, we will assume it proved. what follows? are we to get no more sugar while we smoke? by no means. hard by the stomach lies the _pancreas_, an organ so similar in structure to the salivary glands, that even so minute an observer as kölliker does not think it requisite to give it a separate description. its secretion, which is poured into the second stomach, contains a ferment analogous to that of the saliva, and amounts probably to about seven ounces a day. the food, on leaving the stomach, is next subjected to its influence, together with that of the bile. it helps digest fatty matters by its emulsive powers; it has been more recently supposed to form a sort of _peptone_ with nitrogenized articles also; but, what is more to our purpose, it turns starch into sugar even more quickly than the saliva itself. and even if the reformers were to beat us from this stronghold, by proving that tobacco impaired the saccharifying power of this organ also, we should still find the mixed fluids supplied by the smaller, but very numerous glands of the intestines, sufficient to accomplish the requisite modification of starch, though more slowly and to a less degree. we come now to the second count in the indictment,that tobacco injuriously affects the nervous system, and through it the digestion. the accusation is here more vague and indefinite, and the answer also is less susceptible of proof. both sides must avail themselves of circumstantial, rather than direct evidence. that digestion is in direct dependence upon the nervous system, and that even transitory or emotional states of the latter affect the former, there can be no doubt. it is so familiar a fact, that instances need hardly be cited to prove it. hence we are told, that tobacco, by deranging the one, disorders the other,that nervousness, or morbid irritability of the nerves, palpitations and tremulousness, are soon followed by emaciation and dyspepsia, or more or less inability to digest. we conceive prout, an eminent authority, to be near the truth, when he says of tobacco, the strong and healthy suffer comparatively little, while the weak and predisposed to disease fall victims to its poisonous operation. the hod-carrier traversing the walls of lofty buildings, and the sailor swinging on the yard-arm, are not subject to nervousness, though they smoke and chew; nor are they prone to dyspepsia, unless from excesses of another kind. it has not been shown that tobacco either hastens or delays the metamorphosis of tissue,that it drains the system by waste, or clogs it by retarding the natural excretions. we must turn, then, to its direct influence upon the nervous system to convince ourselves of its ill effects, if such exist. nor has it been proved that the nervous influence is affected in such a way as directly to impair the innervation of the organic functions, which derive their chief impulse to action from the scattered ganglia of the sympathetic system. opium, the most powerful narcotic, benumbs the brain into sleep; produces a corresponding reaction, on awakening; shuts up the secretions, except that of the skin, and thus deranges the alimentary functions. the decriers of tobacco will, we conceive, be unable to show that it produces such effects. the reformers are reduced, then, to the vague generality, that smoking and chewing affect the nerves. students, men of sedentary, professional habits, persons of a very nervous temperament, or those subject to much excitement in business and politics, sometimes show debility and languor, or agitation and nervousness, while they smoke and chew. are there no other causes at work, sufficient in themselves to produce these effects? are want of exercise, want of air, want of rest, and want of inherited vigor to be eliminated from the estimate, while tobacco is made the scape-goat of all their troubles? climate, and the various influences affecting any race which has migrated after a stationary residence of generations to a new country extending under different parallels of latitude, have been reasonably accused of rendering us a nervous people. it is not so reasonable to charge one habit with being the sole cause of this, although we should be more prudent in not following it to excess. the larger consumption of tobacco here is due both to the cheapness of the product and to the wealth of the consumer. but it does not follow that we are more subjected to its narcotic influences because we use the best varieties of the weed