INTRODUCTION. 13 



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 epider- 

 mis 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 almost any other flexible substance. This sub- 

 stance is, especially in the upper or more coloured and glossy 

 parts of the feathers, combined with oils and metallic sub- 

 stances in very minute portions ; but in the down and the 

 light-coloured feathers it is nearly pure. 



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

 portion 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 water- 

 proof from its glossy texture, and (possibly ?) 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 inter- 

 vals between them, but the material is in all cases substan- 

 tially 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 

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



