COVERING OF THE HOUSE. 139 



but it is never real skin ; and this is the reason 

 why it remains a scar. 



OIL GLANDS. No process has ever been 

 devised, so far as I know, by which the outside 

 of a building can be oiled of itself, without 

 manual labor. Nor is it common or necessary 

 to apply oil to a building, except in the form 

 of paint, which is partly oil. 



But the animal frame seems to require fre- 

 quent oiling ; and, in some of the feathered 

 tribes, it is done by the beak. They have a 

 little gland, as it is called, which furnishes 

 them with oil. This oil they press out with 

 their bills, and then apply it to their feathers, 

 which also overlap each other like shingles, 

 that they may the better shed the rain. 



But most other animals, instead of having 

 the oil in a single bag or gland, have it in a 

 thousand little glands, almost too small to be 

 seen by the naked eye, and imbedded in the 

 skin. They are very thick indeed in the skin 

 of the sheep, and hence the wool of a healthy 

 sheep is always quite oily. They are nume- 

 rous, too, about the roots of the hair of most 



