468 
Mr. J. Lewis Bonhote on Moult 
proved, since the white feathers are worn at their edges ; 
these edges do not change colour, but there is a space of 
about J of an inch left white, which is lost by abrasion. 
On the back there is a fairly complete moult, and also under 
the chin and throat, but the new growing feathers are white, 
not black or parti-coloured, and then change to the black 
summer dress. 
All this must he qualified by axioms i. and ii., and 
although I have no notes to that effect, it would not surprise 
me to find new black feathers growing on a bird. But I hope 
I have shown that in some cases this takes place by change 
of colour, and that therefore change of colour is a possible 
phenomenon. As to the physiological process which goes 
on, I am not in a position to write about it at present, but 
should like to draw attention to a paper by M. V. Fatio*, 
in which he shows that an oil is continually making its way 
into the feather from body ; and this is further confirmed 
and proved by Mr. Chad bourne in the paper quoted above, 
both these gentlemen stating that this flow is not due to any 
active agent, but to osmosis, capillarity, or some similar 
action. Most pigments are soluble in ether, alcohol, or 
chloroform, thus proving them to be of an oily nature. 
Now, if it has been proved that oil can make its way up a 
feather, and, further, that all true pigments (black, red, and 
their combinations) are of an oily nature, it necessarily 
follows that pigment can make its way up also. 
I make no claim to any discovery in this matter. M. Fatio 
coloured an oil and caused it to make its way up into the 
barbs and barbules of a feather, in order that he might prove 
that substances of an oily nature could find a passage through 
the feather, entirely disregarding the far more important 
discovery that 'pigment could do so. I may mention briefly 
that his theory (and it is one that apparently holds good 
for several birds) was that pigment was formed in various 
places in the growing feather, and remained there until it 
was diluted by the colourless oil which made its way from 
the body of the bird. 
* Loc. supra cit. 
