in the stoat and ermine, and among birds, in the ptarmigan,
and some other species of Lagopus. How the change from the
autumnal to the winter condition takes place appears not to
be definitely settled in all cases, and accurate observations
are much to be desired. In the case of the Norway hare,
it has been stated that a general moult, including all the
hairs and under fur, takes place and new white hairs are
substituted. The process of moulting is said to begin in
the middle of autumn and is completed before the end of
December, by which time the fur is in its winter condition,
and is closer, fuller and longer than in summer (Naturalists'
Library, vol. vii.). On the other hand, it has been stated
that during the whole of the transformation in the fur no
hairs fall from the animal, and it is attributed to an actual
change in the colour of the hair (Edinburgh Philosophical
Journal, vol. xi. p. 191). In the case of the American
hare, however, some very careful observations have been
made by F. H. Welch. In this animal the long hairs (which
form the pile) become white at their extremities, and in
some of them this whiteness extends through their whole
length. At the same time, new hairs begin to develop and
to grow rapidly, and soon outstrip the hairs of the autumn
pile. From their first appearance these new hairs are white
and stiff, and they are confined to the sides and back of the
body. It is not clear from Welch's account what is the cause
of the whiteness of the tips of the hairs of the autumn coat,
but his figures suggest that it is due to the development
of gas in the interspaces between the keratin bridges and
trabeculae of the hairs. There is nothing to show whether
the pigment persists or is absorbed. Probably it persists.
In this event, the whiteness of the tips will be due to the
scattering or irregular reflexion of the incident rays of
light from the surface of the numerous gas bubbles. In the
case of the ptarmigan the evidence is clear that the existing
autumnal feathers do change, more or less completely, to
white. But the evidence is not conclusive as to whether any part
of the winter condition is additionally produced by moulting.
The condition of albinism thus assumed as a seasonal variation
is never complete, for the eyes at least retain their pigmented
state. The reason of this is readily understood when it is
borne in mind how disadvantageous to the function of sight is
the unpigmented condition of an albino's eyeball; a disadvantage
which would be probably much accentuated, in the cases now under
consideration, by the bright glare from the surface of the
snow, which forms the natural environment of these animals
at the particular period of the year when the winter change
occurs. In some cases, as in all the varying hares, in addition
to the eyes retaining their normal pigmentation, areas similar
in extent and situation to those on the Himalayan rabbits also
retain their pigmentation; and in the ptarmigan there is a
black band on each side of the head stretching forwards and
backwards from the eyeball, and the outer tail feathers are black.
Albinism is restricted to no particular class of the animal
kingdom; for partial albinism at least is known to occur in
Coelentera, worms, Crustacea, Myriapoda, Coleoptera,Arachnida and
fishes. The individuals in which this diminished pigmentation
is found are for the most part those living in caves, and
it is probable that their condition is not truly albinotic,
but only temporary and due to the absence of the stimulus of
light. This may be also true of some of those instances
that have occurred among frogs, in Proteus, and with an
axolotl once possessed by the present writer. This latter
animal was quite white, with the exception of the black
eyeballs. At the end of four weeks after it was first
purchased the dorsal or upper surface of its external gills
developed a small amount of dark pigment. Within the next
few weeks this increased in quantity and the dorsal surface
of the head and of the front end of the trunk began to be
pigmented. The animal died at the end of the eighth week, but
it is possible that had it lived it would have become wholly
pigmented. But, apart from these instances, albinism is known,
according to W. E. Castle, who cites it on the authority of Hugh
M. Smith, to occur among a breed of albino trout, which breed
true and are reared in the State fish-hatcheries of America.
With birds and mammals, however, there is no doubt that complete
albino individuals do occur; and among species which, like the
jackdaw, certain deer and rabbits, are normally deeply pigmented.
Albinism occurs in all races of mankind, among mountainous
as well as lowland dwellers. And, with man, as with other
animals, it may be complete or partial. Instances of the
latter condition are very common among the negroes of the United
States and of South America, and in them assumes a piebald
character, irregular white patches being scattered over the
general black surface of the body. Occasionally the piebald
patches tend to be symmetrically arranged, and sometimes the
eyeballs are pigmentless (pink) and sometimes pigmented (black).
According to A. R. Gunn, of Edinburgh Dniversity, who has
recently been investigating the subject of albinism in
man, there is reason to believe that a condition of piebald
albinism occurs also in Europeans (Scotsmen). He has examined
subjects in which the whole of the hair of the body is
white, but the eyeballs are pigmented, often deeply; and,
conversely, he has seen cases in which the eyes are pink
but the hair is pigmented. The hair and the eyes may be
regarded as skin patches, in which sometimes the one and
sometimes the other is pigmentless. He believes that, were
it not for the generally very pale colour of white-skinned
races, this piebald condition would be as manifest in
them as in negroes, over the whole surface of the body.
In complete human albinoes, albinism is correlated, in addition
to nystagmus, with a peculiar roughness of the skin, making it
harsh to the touch. The skin is also milky-white in appearance.
According to C. J. Sehgmann, there exists among the Papuans
an albinotic race whose skin varies in colour from a
pink-white to that of cafe au lait; the eyes are generally
greenish, hazel or brown, and the hair is tow-coloured. The
skin where unexposed is pinker than that of a normal North
European. Like complete albinoes, this race suffers from
photophobia, and is characterized by the albinotic facies.
Before we can inquire into the cause and meaning of albinism it
will be necessary first to consider the nature Of pigmentation.
It has recently been ascertained that the coloration of
certain sponges is due to the interaction of an oxydizing
ferment, tyrosinase, upon certain colourless chromogenic
substances. In 1901, Otto v. Furth and Hugo Schneider showed
that a tyrosinase could be obtained from the blood of certain
insects, and, acting upon a chromogen present in the blood,
converted it into a pigmentary substance of melanin-like
nature. Hans Przibram also extracted a tyrosinase from the
ink-sac of Sepia, and, causing it to act upon a watery
solution of tyrosin, obtained a black pigment. From the blood of
Bombyx mori, fe. von Ducceshi has also obtained a tyrosinase.
Subsequently (1903) L. Cuenot, in order to explain certain
features in the hereditary transmission of coat colour in
mice, postulated the hypothesis that the grey colour of
the wild mouse (which is known to be a compound of black,
chocolate and yellow pigments) may be due either to the
interaction of a single ferment and three chromogens, or vice
versa, to one chromogenic substance and three ferments.
Since then (1904) Miss Florence Durham has shown that if
the skins of young or embryonic mammals (rats, rabbits and
guinea-pigs) be ground up and extracted in water, and the
expressed juice be then incubated with solid tyrosin for
twenty-four hours, with the addition of a very small amount
of ferrous sulphate to act as an activator, a pigmentary
substance is thrown down. The colour of this substance
is that of the pigment in the skin or hairs of the animal
used. Miss Durham interprets her results as indicating that the
skin of these pigmented animals normally secretes one or more
tyrosinases. The same result was obtained from the skins of
some unhatched chickens. The skins of albinoes gave no results.
Not only have such resuits been obtained with sponges,
Insects, cephalopods, birds and mammals, but Em. Bourquelot
and G. Bertrand have shown that certain fungi, the tissues
of which, when exposed to the air by injury, become
immediately coloured, do so owing to the action of tyrosinase
upon one or more chromogenous substances present in the
plant. We may conceive, then, that a pigmented animal
owes its colour to the power that certain tissues of its
body possess to secrete both tyrosinases and chromogenic
substances. And the period at which this process is most
active is at birth, or preceding it or immediately succeeding
it. In spite of the inquiry being only in its initial stages,
there is already good evidence to believe that Cuenot's
theory is correct, and that an albino is an individual whose
skin lacks the power to secrete either the ferment or the
chromogen. It forms one but not both of these substances.
A moment's consideration, however, will show that, while
an albino may be an individual in which one or more of
the complementary bodies of pigmentation are absent, a
pigmented animal is something more than an individual which
carries all the factors necessary for the development of
colour. For it must be borne in mind that animals are not only
coloured but the colour is arranged in a more or less definite
pattern. The wild mouse, rat and rabbit are self-coloured,
but the domesticated forms include various piebald patterns,
such as spotted forms among mice, and the familiar black and
white hooded and dorsal-striped pattern of some tame rats.
Colour, therefore, must be correlated with some determinant
(determining factor) for pattern, and it cannot, therefore,
exist alone in an animal's coat. And we must conceive that
each kind of pattern---the self, the spotted, the striped,
the hooded and all others---has its own special determinant.
Given the presence of all the necessary determinants for
the development of pigment in a mammal's coat, some or all
of the hairs may bear this pigment according to the pattern
determinants, or absence of pattern determinants, which the
cells of the hair papillae carry. And this brings us to
the question as to whether in a piebald animal the pigmented
hairs are in any way different from the pigmentless or white
hairs. No adequate investigation of this subject has yet
been made, but some observations made by the author of this
article, on the piebald black and white rat, show that
differences connected with the microscopic structure exist.
There is thus evidence that colour is correlated with other
factors which determine pattern. And this leads to the
inquiry as to whether albinoes ever exhibit evidence that they
carry the pattern determinants in the absence of those for
pigmentation. For it is to be expected a priori that, since
albinoes were derived from pigmented progenitors and may at
any time appear, side by side with pigmented brothers, in
a litter from pigmented parents, they would be carrying the
pattern determinants of some one or other of their pigmented
ancestors. Now we know, from the numerous experiments in
