174 Fatio on Feathers — their Decoloration. 



the moisture and light which are necessary to effect a solution 

 of the latent pigment. At the same time extravasation occurs 

 in the hidden parts of the feather, likewise producing a de- 

 coloration towards the extremities moving in a contrary 

 direction and encountering the other action." 



" Of these two processes of decoloration, the second some- 

 times overpowers the first, and under certain conditions' it 

 sometimes happens that a feather becomes gradually decoloured 

 from the summit to the base. As is the case with extravasa- 

 tion, the coloration is always more rapid in mixt feathers. 

 The quickest coloration is most often due to abundance of 

 the greasy matter in a bird, aided by favourable conditions of 

 atmospheric moisture and temperature. The changes are also 

 often rendered more striking by an exceptionally rapid fall of 

 the fragile tips, which mask, while they remain, the transition 

 that has taken place in adjacent parts." The occurrence of 

 albinism, which is natural in some birds, may be accounted for 

 by the accidental operation in others of the causes just ex- 

 plained. 



M. Fatio thinks that under the influence of violent emotion 

 an unusual influx of greasy matter may occur, and under suit- 

 able conditions of temperature and moisture, may give rise to a 

 sudden appearance of albinism. 



" The extravasated coloured dust must not be confounded 

 with the true external colouring which the feathers of some 

 birds exhibit. Many species of different orders show, in fact, 

 accidentally or regularly on certain parts of their bodies, most 

 frequently on their lower surfaces, different colorations, more 

 or less concentrated, and more or less persistent, resulting from 

 friction against certain mineral or vegetable bodies of which 

 they are particularly fond. This external painting has some- 

 times given rise to the creation of false species. It arises most 

 frequently from the soil on which the bird lives, the food it ob- 

 tains, and the kind of life it leads. M. Meves, in a memoir 

 which was translated by Gloger, and inserted in the " Journal of 

 Ornithology" (Journal filr Ornithologie), studied the brown and 

 orange coloration of the vulture (Gypaetos). of the south. He 

 described this coloration as external, and capable of removal 

 by an acid wash, and he attributed it to the repeated bathings 

 of the bird in ferruginous springs. Eugene von Homey er also 

 noticed a brown external coloration amongst the cranes in 

 their nesting time in the north, and he ascribed it to the marshy 

 soil with which the birds covered themselves by means of their 

 beaks. Meves has likewise noticed the same thing, and adds 

 that it is perceptible (comes off?) when touched. Many ducks 

 also acquire a rosy tint on the belly, from the vegetation on 

 which they rest. Some small birds in like manner become of 



