The earthworm's favorite diet is leaves and he has a way of cooking them. It is not quite like our way of cooking beet or dandelion leaves, but it answers the same purpose--it partially digests them. In glands, in his "mouth," he secretes a fluid which, like our saliva, contains an alkali. But the earthworm's alkaline solution is much stronger, and when he covers a fresh green leaf with it--as he is usually obliged to do in Summer when there are so few stale vegetables, the kind he prefers, in his market--the leaf quickly turns brown and becomes as soft as a boiled cabbage. Of course, there are always dead leaves in the woods, and these, which even the cow with her fine digestive outfit cannot handle, are a delight to the earthworm; for he also has a much larger supply of pancreatic juice than the higher animals, and this takes care of the leaves after he has swallowed them. He swallows bit by bit; just like a nice little boy who has been taught not to bolt his food. The acids in the earthworm's "stomach," acting on the leaves, help make other acids which remain in the soil after it has passed through the earthworm's body and help dissolve those fine grains of sand which make your bare feet so gritty when mud dries on them. And, not only that, but this coating of soil lying upon the bed rock hastens its decay; for the earthworm's burrow runs down four to six feet, sometimes farther. Besides the soil he thus grinds up and fertilizes so well with leaf-mould--what your text-book on agriculture calls "humus"--the earthworm does a lot of useful grinding in connection with the building of his house. He begins, as we do, by digging the cellar; but there he stops, for _his_ house is _all_ cellar! He makes it in two ways: (1) By pushing aside the earth as he advances; (2) by swallowing earth and passing it through his body, thus making the little mounds you see on the surface. THE EARTHWORM SYSTEM AT PANAMA A principle similar to his swallowing operations is frequently employed in engineering; as in making the Panama Canal, where dredging machinery dug out swamps and pumped the mud through a tube into other swamps to fill them up and help get rid of the mosquitoes. In pushing the earth away the worm uses the principle of the wedge, stretching out his "nose"--as you have often seen him do when crawling--and poking it into the crevices in the ground; much as the wheat roots poke _their_ little noses through the fertile soil the earthworm makes. And, as in human engineering and the work of the ant, the earthworm doesn't throw the dirt around carelessly. He casts it out, first on one side and then on the other; using his tail to spread it about neatly. THE TILING IN THE EARTHWORM'S HOUSE