Evening star. [volume] (Washington, D.C.) 1854-1972, 1904-01-09
COLOR CHANGE IN ANIMALS.
Theories Concerning the Whitening IN
Winter.

From Nature.
The winter whitening of animals, though
OF intense interest to zoologists, Is very i'm.
perfectly understood. Most writers arS
satisfied to believe that this color change
was perfected somehow under the action
of natural selection for the protective pur.
poses Of adaptation to environment I1
origin they leave as an unsolved problem.
1 find, however, that the change has q
deep physiological significance. There II.
for instance in mammals definite SO.
quence In which the various parts OF the
body whiten. The sequence corresponds to
the summer accumulation of fat in the
ponniculus adiposus. Thus the belly
where peripheral fat is thickest, Is per.
manently white, and the rump where also
fat accumulates thickly, is usually the first
part to whiten in winter. Many northern
mammals and birds are not usually re.
garded of the winter whitening category,
are lighter in winter than in summer Tho
wilderness or white patches assumed In the
former season correspond to the fat tracts,
so that these species may be regarded az
subject to the same process. In the north
ern summer most animals accumulate tat.
always in a definite manner as regards the
regions where 1t Is deposited This fat ~
indicative of deficient oXidizatfon ana OF
sluggish metabolism, and the process Of III
accumulation is. therefore, one of atrophy.
The fat accumulation and atrophy are most
marked In autumn, at which season meta
boliSm is therefore lowest. With the onset
of winter cold the atrophy may extend to
the hairs. Their pigment las observed BY
MetchnikofD is then removed, always. how.
ever, commencing with those parts where
peripheral fat Is thickeSt, and atrophy,
therefore, greatest. Should there be
change of coat at this time the hairs
are Influenced by the same conditions. In
very cold countries they come up white alt
over the animal; in more temperate regions
the parts only where fat is thickest are
white.
Although a pigmented hair can thus uns
dergo atrophy and loss of pigment, l know
of NO case where the color is replaced.
Animals once whitehead remain so until the
spring moult. These facts apply broadly to
birds and mammals, but the hare and
stoat are the species which / have studied
especially. Similar laws govern a great
deal of the distribution of the white color
throughout the vertebrate phylum. wherein
the connection between white color and the
peripheral fat tracts Ghus indicating local
atrophy) may be widely traced. Thus do
nestle animals, nearly all of which are
priced most for their power of accumulat.
ing fat exhibit strong tendency to the
development of white patches. In both
these and in wild animals the belly. where
occurs the principal fat tract, is the most
frequently white part; next follow the
rump and parts of the neck, of the limbs
and of the head.
Marked exceptions are no doubt frequent
ly due to unusual arrangements of the
panniculus adiposus. Thus in the badger,
a representative of a family In which the
back is usually winter than the belly, find
a correspondngly exceptional arrangement
of the fat tracts. The white of the head
the blaze" of horses, the facial stripes Of
the badger-often affects regions not of fat
accumulation, but where the skin tmmedf-
ately overlies bone and membrane 6rontals
and nasals and zygomatic arch), which thus
seem to produce an atrophy similar to that
caused by underlying fat. In many ami
mails the hair atrophy assumes the form
not of whitening but of badness. Marine
mammals are hairless in proportion to tho
development of their peripheraI fat layer;
fattening cattle lose their hair, while the
badness OF man corresponds in position
to the blaze" of horses, and the bare
buttocks of monkeys to the white rumpS
of other animals.
Yellow and red frequently follow the
same rules of distribution as white The1
are well known to be fat pigments