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"N EARLY all the higher or mammiferous animals," Uncle Paul continued, "such as the dog, cat, wolf, horse, have only one digestive pouch—a stomach—where the alimentary substances are dissolved and made fluid, so as to enter the veins and be turned into blood, by which all parts of the body are nourished. But the ox, goat and sheep—the cud-chewers, in short—have four digestive cavities, which I will tell you about later. I will tell you how, in the pasture, these animals hastily swallow almost unchewed grass and put it by in a large reservoir called a paunch, from which it comes up again afterward in a season of repose, to be rechewed at leisure in small mouthfuls.
"Well, birds are fashioned in a similar way, as far as eating is concerned. Not being able to chew, as they have no teeth, they swallow their food without any preparation, nearly as the beak has seized it, and amass a quantity of it in a spacious stomach, just as the ox does in his paunch. From this reservoir the food passes, little by little, into two other digestive cavities, one of which immerses it in a liquid calculated to dissolve it, and the other grinds and triturates it better than the best pair of jaws could do. There takes place a kind of chewing, it is true, only the food, instead of returning to its beak, where teeth are lacking for its thorough mastication, continues its journey, and on the way comes to the triturating machine. Birds, then, are generally provided with three digestive cavities.
"The first is the crop, situated just at the base of the neck. It is a bag with thin and flexible walls, its size proportioned to the resistant nature of the food eaten. It is very large in birds that feed on grain, especially the hen, and is medium-sized, or even wholly wanting in those that live on prey, which is much easier to digest than dry and hard seeds. In the crop, the food swallowed in haste remains hours and even days, as in a reservoir; there it softens somewhat, and is then submitted to the action of the other digestive pouches. The crop corresponds in a certain sense to the bag in which the pelican stores up his fishing; it represents also the first stomach of the ox and the other cud-chewers or ruminants.
"Next to the crop is the second enlargement, called the succenturiate ventricle, of small capacity but remarkable for a liquid of a bitter taste that oozes in fine drops through its walls and moistens the food as it passes. This liquid is a digestive juice; it has properties of dissolving the alimentary substances as soon as trituration has done the greater part of the work. The food does not remain in this second stomach; it merely passes through to become impregnated with the digestive juice.
"The third and last stomach is known as the gizzard. It is rounded and slightly flattened on both sides, like a watch-case, and is composed—especially in birds that live on grain—of a very thick, fleshy wall, lined on the inside with a kind of hard and tenacious leather which protects the organ from attrition. Finally, it is to be noted that at the same time the bird is swallowing grain it takes care also to swallow a little gravel, some very small stones which, away down in the gizzard, will perform the office of teeth."
"I know what the gizzard is," volunteered Emile. "When they are cleaning a chicken to cook, they take out of the body something round that they split in two with a knife; then they throw away a thick skin all wrinkled and stuffed with grains of sand, and the rest is put back in the chicken."
"Yes, that is the gizzard," said Uncle Paul. "Let us complete these ideas got from cooking. The bird, not having in its beak the molars necessary for grinding, as in a mill, the seeds that are hard to crush, supplies its gizzard with artificial teeth, which are renewed at each repast; that is to say, it swallows little pebbles. The grain, softened in the crop and moistened with the digestive juice during its passage through the succenturiate ventricle, reaches the gizzard mixed with the little stones that are to aid the triturating action. The work then performed is easy to understand. If you pressed in your palm a handful of wheat mixed with gravel, and if your fingers, by continual movement, made the two kinds of particles rub vigorously against each other, is it not true that the wheat would soon be reduced to powder? Such is the action of the gizzard. Its strong, fleshy walls contract powerfully and knead their contents of sand and seeds without suffering damage themselves from friction, because of the tough skin that lines their inside and protects them from the roughness of the gravel. In such a mill the hardest kernels are soon reduced to a sort of soup.
"To make you understand the prodigious power of the gizzard, I cannot do better
than relate to you certain experiments performed by a learned Italian, the abbot
Spallanzani. A century ago the celebrated abbot, while pursuing his researches
on the natural history of animals, caused a number of hens to swallow some
little glass balls. 'These balls,' he said, 'were sufficiently tough not to
break when thrown forcibly onto the ground. After remaining three hours in
the hen's gizzard they were for the most part reduced to very tiny pieces
with nothing sharp about them, all their edges having been blunted as if
they had been passed through a mill. I noticed also that the longer these
little glass balls remained in the stomach, the finer the powder to which
they were reduced. After a few hours they were broken into a multitude of
vitreous particles no larger than grains of
"A stomach that can grind glass balls to powder," commented Jules, "is certainly a first-rate mill."
"You shall hear something still more remarkable," returned his uncle. "Wait. 'As
these balls,' continued the abbot, 'were polished and smooth, they
could not create any disturbance in the gizzard.' So he was curious to see what
would happen if sharp and cutting bodies were introduced. 'We know,' he says, 'how
easily little pieces of glass, broken up by pounding, tear the flesh. Well, having
shattered a pane of glass, I selected some pieces about the size of a pea and
wrapped them in a playing card so they would not lacerate the gullet in their
passage. Thus prepared, I made the cock swallow them, knowing that the covering
of card would break on its entrance into the stomach and leave the glass free to
act with all its points and sharp
"With all those little pieces of glass in its stomach," said Jules, "the bird must surely have died."
"Not a bit of it. The bird would have come out all right if the experimenter had not sacrificed it to see the result. The cock was killed at the end of twenty hours. 'All the pieces of glass were in the gizzard,' the abbot tells us, 'but all their sharp edges and points had disappeared so completely that, having put these fragments on my palm, I could rub them hard with the other hand without inflicting the slightest wound.
"So the bird that is made to swallow pieces of broken glass," said Jules, "grinds them up without injury and without even a scratch, while we could not so much as handle the dangerous stuff with the tips of our fingers without wounding ourselves. This power of the gizzard is really inconceivable."
"What follows is still more surprising," resumed Uncle Paul. "Spallanzani continues: 'The experiments with glass not having done the birds any harm, I performed two others that were much more dangerous. In a leaden ball I placed twelve large steel needles so that they stuck out of the ball more than half a centimeter, and I made a turkey swallow this ball, bristling with points and wrapped in a card; and it kept the ball in its stomach for a day and a half. During this time the bird showed not the slightest discomfort, and in fact there could have been none, for on killing the bird I found that its stomach had not received the slightest wound from this barbarous device. All the needles were broken off and separated from the leaden ball, two of them being still in the gizzard, while the other ten had disappeared, ejected with the excrement.
"You see, my little friends, a bird's gizzard is the most wonderful organ of trituration in the world. What are the best-equipped jaws in comparison with this strong pouch which, without suffering so much as a scratch, reduces glass to powder and breaks and blunts steel needles and lancets? You can understand now with what ease the hardest seeds can be ground when the gizzard of the granivorous bird presses and rolls them pell-mell with small stones."
"Where glass and steel are broken up," said Emile, "grain ought to turn to flour as well as in a mill."