“That greasy wart might be called a sort of pomatum pot,” suggested Emile.
“It is a pomatum pot, if that comparison pleases you. Thus greased, thus anointed with pomatum, feather by feather, the duck furnishes no foothold for moisture, because, as you all know, water and [[100]]oil do not mix, and from an oiled surface drops of water run off without wetting it. Such is the secret of the duck’s keeping itself dry when immersed in water.”
“That is one of the most curious things I ever heard of,” declared Jules, “and one that I shouldn’t have known anything about for a long time if it hadn’t been for Uncle Paul. Should I ever have guessed that the duck presses a certain wart on its rump to get the grease for oiling its feathers?”
“The duck’s secret is known to all birds without exception; all have this oil-sac on the rump, and obtain from it the oil for giving luster to their plumage and making it impervious to wet; but aquatic birds are more abundantly provided in this respect. And it is only right that those most exposed to dampness should have the largest reservoir of this oily coating.”
“In all birds the fattest part is always the rump,” said Louis. “Grease gathers there by preference, no doubt, to maintain the store of oil in the oil-sac?”
“Evidently. It is in this storehouse that the oil attains its perfect state and becomes the finished product that oozes from the sac. As to the making of it in the first place, nearly all parts of the body take part; and as the swimming bird uses a great deal of this pomatum, the result is that the palmipede tends to fatness and, as it were, sweats grease: witness the plump duck and goose, which carry under the breast a heavy, fat swelling. As a general rule, the web-footed fowl of our poultry-yards is [[101]]analogous to the pig: it is a fat-factory. We divert to our own use the excess of fat accumulated primarily for the supply of the oil-sac on the rump and the maintenance of the luster that distinguishes the plumage.
“The palmipede, you see, is admirably protected against wet. Neither rain nor the finest drizzle can penetrate the first covering of feathers, always kept, as it is, well coated with the varnish laid on by the point of the beak. The bird can plunge into the deepest water, swim on its surface, or sleep there cradled by the waves, and the wet will not reach it. Neither will cold affect it, for under this outer covering is found a second, designed for resisting inclement weather and made of what is most efficacious for preserving the heat of the body. This under-clothing of aquatic birds is a down so delicate and soft that, unable to compare it with anything else, we have given it a special name, that of eiderdown. In its proper place I will come back to this down. For the present let us confine ourselves to a general survey of the palmipedes, and of the duck in particular.” [[102]]