different alimentary substances in hollow spheres of silver, pierced
with small holes. These were swallowed, and after remaining some time
in the stomach, the contents were found dissolved. The great agent of
solution is the gastric juice, which possesses a very strong solvent
power. This juice is secreted by the arteries of the stomach; it may
be collected in considerable quantity, by causing an animal that has
been fasting for some time, to swallow small hollow spheres, or tubes
of metal filled with sponge.

This liquid does not act indiscriminately upon all substances; for if
grains of corn be put into a perforated tube, and a granivorous bird
be made to swallow it, the corn will remain the usual time in the
stomach without alteration; whereas if the husk of the grain be
previously taken off, the whole of it will be dissolved. There are
many substances likewise which pass unaltered through the intestines
of animals, and consequently are not acted upon by the gastric juice.
This is the case frequently with grains of oats, when they have been
swallowed by horses entire, with their husks on. This is the case
likewise with the seeds of apples and other fruits, when swallowed
entire by man; yet if these substances have been previously ground by
the teeth, they will be digested. It would appear therefore, that it
is chiefly the husk or outside of these substances which resists the
action of the gastric juice.

This juice is not the same in all animals; for many animals cannot
digest the food on which others live. Thus sheep live wholly on
vegetables, and if they are made to feed on animals, their stomachs
will not digest them: others again, as the eagle, feed wholly on
animal substances, and cannot digest vegetables.

The accounts of the experiments made on gastric juice are very
various: sometimes it has been found of an acid nature, at other
times not. The experiments of Spallanzani show, however, that this
acidity is not owing to the gastric juice, but to the food. The
result of his experiments, which have been very numerous, prove, that
the gastric juice is naturally neither acid nor alkaline. No
conclusion, however, can be drawn from these experiments made out of
the stomach, with respect to the nature of the gastric juice; nor do
the analyses which have been made of it throw any light on its mode
of action. But, from the experiments which have been made on
digestion, in the stomach, particularly by Spallanzani,