We have as yet become acquainted with no satisfactory series of experiments upon tobacco analogous to those which have been made of some articles of food.

The opponents of tobacco, upon whom we consider the burden of proof to rest, in the absence of any marked ill effects palpable in so large a consumption of the herb, are thus reduced to generalities.

Tobacco is said to produce derangement of the digestion, and of the regular, steady action of the nervous system.  These effects must be in a measure connected; but one distinct effect of tobacco is claimed, upon the secretions of the mouth, with which it comes into direct contact.  It is said to cause a waste and a deterioration of the saliva.  Let us examine this first.

The waste of saliva in young smokers and in immoderate chewers we admit.  The amount secreted by a healthy man has been variously estimated at from one and a half to three pounds per diem.  And it certainly seems as if the whole of this was to be found upon the vile floors of cars, hotels, and steamboats.  The quantity secreted varies much with circumstances; but experiments prove the quality to be not affected by the amount.

To show how the deterioration of this fluid may affect digestion, we must inquire into its normal physiological constitution and uses.  Its uses are of two kinds:  to moisten the food, and to convert starch into sugar.  The larger glands fulfil the former; the smaller, mostly, the latter office.  Almost any substance held in the mouth provokes the flow of saliva by mechanical irritation.  Mental causes influence it; for the thought of food will “make the mouth water,” as well as its presence within the lips.  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.