INTRODUCTION. 
Xlll 
zard.^ Even in the granivorous tribes is found this solvent ; but in them it 
operates but slowly, in the dissolution of flesh, and even on grain, seeds, 
berries, fruits, and vegetables ; it appears to act with a very small degree of 
dissolving power, and rather to assist the preparation of the food into 
chyle, after it has been comminuted by the action of the muscles of the 
gizzard. Spallanzani filled porous, or partially open tubes, and some- 
times hollow spherules, having small openings, with raw flesh, and thrust 
them into the stomachs of fowls, turkeys, ducks, geese, and pigeons ; and 
he found that, after the flesh had remained under the operation of the 
gastric fluid upwards of thirty-six hours, it had lost nearly half of its 
weight, grown more tender than in its natural state, and changed to a 
cineritious colour ; evident marks of solution, and of the weak action of 
the gastric fluid in these birds.® 
In the granivorous birds, their food is first softened by the liquor 
flowing from the glands in the oesophagus, then triturated by the violent 
approximation of the muscles in the gizzard, and, at length, penetrated by 
the gastric fluid, which destroys its texture, dissolves its particles, and fits 
it for the nutrition and absorption of the animal. In the carnivorous and 
piscivorous kinds, the muscles of the stomach perform but a little part of 
digestion ; in them it depends principally on the efficacy of the gastric 
’ The stomach of the Cuckoo has been described as covered internally with bristly spiral 
hairs. I have dissected several, and, I must confess, that in neither of those, which I have 
inspected, have I been enabled to discover any hairs, attached to the internal coat of the gizzard, 
although there were, in one of them, numerous hairs of the rough beetle. 
® In those birds, of which animal substances are the proper food, the gastric fluid dissolves, 
most rapidly, the flesh exposed to its action. In two hours, Spallanzani found it, from the 
stomach of crows, changed in colour, the surface become flabby, and the cohesion of the parts 
destroyed, and a dark covering of jelly surrounded the flesh. He describes the operation of this 
menstruum as first softening the texture, and changing the colour ; then succeeds a decomposition 
of the parts, and next a transmutation of the flesh into a kind of jelly, differing in taste froi® 
that of flesh. 
