“And only the other day,” put in Louis, “I kicked out of my way a jaw-bone that was lying in the road. How gladly should I have looked at it closely if I had known all these things!”
“Ignorance always kicks things aside like that, my boy, but science is interested in everything, knowing that it can always learn something. But let us return to the teeth of the carnivorous animals and examine those of the wolf.
“Here the irregularities of the nutmeg-grater, the parallel ridges of the file, and the roughness of the millstone would be of no use, since the animal’s food is to be torn into shreds and not chewed into paste. For the wolf’s food cutting blades are needed—sharp scissors which are hard enough not to become blunt. Hence the working edges of the wolf’s teeth are not flat like millstones, but shaped rather like pointed chisels. The ivory forms the central body of the tooth, making it tough and strong, while the enamel, harder but more brittle, is spread as a continuous layer over the tooth and furnishes the requisite cutting edges. In like manner a skilful cutler, when he wishes to make an edged tool that will cut well and [[12]]at the same time withstand violent blows, makes its central mass of iron, a tough material that bears considerable violence without injury, but is not hard enough to furnish a keen cutting edge. He then overlays it, to obtain such an edge, with fine steel, which combines excessive hardness with the fragility of glass. The best that man can contrive in the making of edged tools is met with in perfection in the teeth of carnivorous animals.”
“If I understand you, then,” said Jules, “ivory, which is not so hard as enamel, but less brittle, forms the interior of the teeth of carnivorous animals, and enamel, which is harder and more brittle, forms the outside layer. Ivory makes the teeth strong; enamel makes them cut.”
“Yes, that is it.”
“Now, I don’t know which is the more wonderful, the donkey’s or the wolf’s set of teeth.”
“Both are wonderful, as both are admirably adapted to the kind of work they have to do.”
“What surprises me most,” Emile interposed, “is that a lot of things we should never pay any attention to turn out to be very interesting when Uncle Paul explains them to us. I never should have thought that the time would come when I should listen with pleasure to the history of a tooth.”
“Since that interests you,” said Uncle Paul, “I will continue the subject a little further and will tell you about human teeth, about yours, my boy, so white and so well arranged, and so admirably adapted for biting a slice of bread and butter.” [[13]]