364 M.V. Fatio on the Coloration of Feathers. 
ends of all the feathers; the latter, torn off by friction at each 
movement of the bird, by degrees make way for the coloration 
manifested in other feathers beneath them. 
During this time the lowest parts of the feather are gradu- 
ally decolorized, not, as might be supposed, in consequence of 
an ascending current of colouring matter, but simply by the 
fall of the greater part of the coloured downy barbules. 
All this takes place without any introduction of new blood, 
without any resurrection of the ‘soul of the feather,” and solely, 
as I have just said, under the influence of moisture externally 
and of the fat in the interior. I have produced and studied 
under the microscope both the development of the cortical sub- 
stance and the internal solution of the different pigments in the 
barbs and barbules. 
Conditions of climate and food produce varieties in nature, 
just as the different influences and the more or less abnormal 
diet to which we subject birds in captivity cause their plumage 
to vary. We may, for example, obtain albinism, either by an 
impoverishment of the blood so that it may no longer furnish 
colouring matters to the feathers, or by a complete extravasation 
of all the internal pigment. Nevertheless, although the solution 
takes place everywhere in the: same way, the coloration is not 
developed in the same manner in all feathers. 
Bogdanow *, who has occupied himself with the chemical 
solution of the pigments of feathers, has distinguished in them 
two groups, in accordance with differences in their pigmentation. 
He has given the name of optical feathers (optiques) to those 
which always furnished him with a brown pigment and owed 
their variety of colours to light alone; and that of ordinary 
feathers (ordinaires) to those which contained variously coloured 
pigments. I have retained this primitive division, which the 
microscope has shown to be natural; but a deeper study has 
forced me to establish two new subdivisions—the mized feathers 
(mixtes), dependent on the ordinary feathers, and the enamelled 
feathers, dependent on the optical. The comparative distribu- 
tion of the cortical substance, combined with the different 
pigmentation, give these feathers their principal distinctive 
characters. 
In the ordinary feathers, which contain various pigments, it is 
the barbs that possess the thickest layer of cortical substance. 
These barbs, in swelling, throw off their useless barbules, and 
in spring form as it were clubs, of which the coloration is the 
same both by transmitted and reflected light. These first fea- 
thers present plenty of brilliancy of colour, but never reflections. 
* Etude sur les Causes de la Coloration des Oiseaux (Revue Zoolo- 
gique, 1858, vol. x. p. 183). 
