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 pr