92 OUR HUMBLE HELPERS 



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 should n'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 ob- 

 tain 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 damp- 

 ness 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 palmi- 

 pede tends to fatness and, as it were, sweats grease : 

 witness the plump duck and goose, which carry un- 

 der the breast a heavy, fat swelling. As a general 

 rule, the web-footed fowl of our poultry-yards is 



