M. V. Fatio on the Coloration of Feathers. 363 
A feather grown in autumn becomes modified in the spring, 
if it is not renewed; but at the same time it passes by degrees 
from a death which was only apparent to a more and more real 
death, until a moment will arrive when it must be expelled and 
replaced by another, presenting certain forms and proportions 
and a determinate coloration. 
At the approach of cold, a new feather, longer and warmer 
because it has been less worn, comes to replace the old one; in 
the spring a more brilliant plumage decorates the bird, which is 
preparing for its nuptials. 
When, in the spring, a bird cannot cover itself with a new 
clothing, it refreshes its old plumage by picking off the worn ends 
and retaining what still remains good. It is precisely this refresh- 
ing, and the new tint thus produced, that I have more particu- 
larly endeavoured to study in the present memoir. I have 
attempted, in taking up the question, always to reproduce arti- 
ficially what I supposed must have taken place in nature. 
A new coloration may appear in a feather, slowly, and even 
commencing in the autumn, or more rapidly, only in the spring; 
it may also consist in a simple augmentation of the intensity of 
the former coloration, or be in complete contrast with it. 
The external or internal conditions which may act upon the 
feather are the humidity of the air, temperature, light, movements, 
and the grease of the bird. The modifications produced by these 
agents are the various development of certain parts, the solution 
and diffusion of the internal pigment, and the rupture of the ex- 
ternal parts. 
The humidity of the air causes the cortical substance of a 
feather to swell, and thus facilitates the communication between 
the constituent cells and fibres. A colourless liquid fat, arriving 
either by the interior or the exterior of the feather, dissolves the 
latent colouring fatty matter in the centres; the intensity of 
the colour is then simply augmented in certain cases, whilst in 
others the old colour is replaced and driven outwards by the 
new one, which spreads and forces it to become extravasated 
throughout in the form of an external powder. A slightly ele- 
vated temperature facilitates these chemical actions; winter 
slackens them; great cold arrests them almost entirely. Light 
seems, as it were, to direct the deposit towards those surfaces 
which are most exposed to it. 
A feather thus becomes coloured more or less rapidly, but 
always from the periphery to the centre, as the extreme parts of 
the new feather are the first and the most exposed to the in- 
fluences of the circumambient air. 
Moisture, which in course of time injures the cortical sub- 
stance which it at first inflated, weakens and deteriorates the 
