40 INTRODUCTION. 



converge so naturally, and with so perfect agreement, to the sur- 

 face which they cover, that no line of separation can be traced. 



The feathers of birds, the coverings of the featherless parts, 

 and even the beaks and claws, are all, chemically speaking, formed 

 of nearly the same materials ; and nearly the same with the hair 

 and cuticle of all animals, and even with the epidermis which 

 covers living shells. This material is coagulated albumen, or 

 nearly the same substance as white of egg when consolidated by 

 heat, in which state it better resists the action of water than al- 

 most any other flexible substance. This substance is, especially 

 in the upper or more coloured and glossy part of the feathers, 

 combined with oils and metallic substances in very minute por- 

 tions ; but in the down and the light-coloured feathers it is nearly 

 pure. 



The under part of the clothing feathers, and also a small por- 

 tion of almost all feathers near the tube or barrel, consists of 

 down, but the exposed surfaces, even of the softest feathers, are 

 smoothed so as to throw off the water. This is the case even in 

 those water-birds which pass the greater part of their time with 

 the under part of the body immersed in water. On them, the 

 down is abundant in proportion as the habits of the birds expose 

 them to cold ; and the external surface is waterproof, from its 

 glossy texture, and (possibly F) also from the oil with which the 

 bird anoints it by means of its bill : but in all birds there is an 

 external surface, adapted to prevent decomposition, and an inner 

 downy matter, as a protection against changes of temperature. 

 The down is partly on the root-ends of the feathers, and partly 

 on the skin in the intervals between them, but the material is in 

 all cases substantially the same ; the difference is in the form, or 

 in the colour, which generally approaches nearer to white in the 

 down than in the feathers. When the bird remains all the year 

 round in situations where there are great differences in the heat 

 of the seasons, the down increases in quantity during winter ; 

 and when birds of a warmer climate are domesticated in a colder 

 one, they become more downy. The form which the down as- 

 sumes is often characteristic of the habits of the bird. In the 

 Ostrich there is none ; in some birds it is a mere tuft at the origin 

 of the webs, in others it is a second feather originating there ; 

 and there are all the intermediate states in different birds, and 

 very considerable seasonal differences in the same bird. 



Different birds find their food in different states, both of the 

 atmosphere and the waters ; and very beautiful corresponding 

 differences in their plumage may be traced. The plumage upon 

 the Haven, which braves the storm in the wilds, is very different 

 from that of the gallinaceous or poultry races, which a slight 

 shower drives to their cover or their perch ; and Ducks and other 



