heredity which have resulted since the rediscovery of Mendel's
principles, that an individual may carry a character in one of two
conditions. It may be carried as a somatic character, when it
will be visible in the body tissues, or it may be carried as a
gametic character, and its presence can only then be detected
in subsequent generations, by adequately devised breeding tests.
With regard to pattern, the evidence is now clear that
albinoes may carry the determinants in both these ways.
So far as they are carried gametically, i.e. by the
sex-cells, it has been shown by Cuenot and G. M. Allen for
mice, by C. C. Hurst for rabbits, and by L. Doncaster and
G. P. Mudge for rats, that in a cross between a coloured
individual of known gametic purity and an albino, the
individuals of the progeny in either the first or second, or
both generations, may differ, and that the difference in some
cases wholly depends upon the aihino used. It has been shown
that the individuals in such an offspring may bear patterns
which never occurred in the ancestry of the coloured parent,
but did in that of the albino; and, moreover, if the same
coloured parent be mated with another individual, either
albino or coloured, that their offspring may never contain
members bearing such patterns. The particular pattern
will only appear when the coloured parent is mated with
the particular albino. And yet the albino itself shows no
somatic pattern or pigment. So clear is the evidence on
this point that any one adequately acquainted at first hand
with the phenomena, by employing an albino of known gametic
structure and mating it with a coloured individual, also
of known gametic constitution, could predict the result.
With respect to albinoes carrying pattern as a visible somatiu
character, i.e. in the body cells, no definite evidence
has as yet been published. But W. Haacke has described a
single albino rat, in which he states that the hairs of the
shoulder and mid-dorsal regions were of a different texture
from those of the rest of the body. And it is possible
that this albino, had it developed colour, would have been
of the piebald pattern. But the author of this article has
quite recently reared some albinoes in which the familiar
shoulder hood and dorsah stripe of the piebald rat is
perfectly obvious, in spite of the absence of the slightest
pigmentation. The hairs which occupy the region which in
the pigmented individual is black, are longer, thinner and
more widely separated than those in the regions which are
white. As a result of this, the pink skin is quite visible
where these hairs occur, but elsewhere it is invisible. Thus
these albinocs exhibit a pattern of pink skin similar in form
with the black pattern of the piebald rat. Moreover, some
of the albinoes possess these particular ``pattern'' hairs
all over the body and obviously such individuals are carrying
the self pattern. There are other details into which we
cannot here enter, but which support the interpretation put
upon these facts, i.e: that these particular albinoes are
carrying in the soma the pattern determinants simultaneously
with the absence of some of the factors for pigmentation.
Not only do albinoes thus carry the determinants for pattern,
but it has been known for some time that they also carry
gametically, but never visible somatically, the determinants
for either the ferment or the chromogen for one or more
colours. L. Cuenot was the first to show this for albino
mice. He was able by appropriate experiments to demonstrate
that when an albino is derived (extracted) from a coloured
ancestry, and is then crossed with a coloured individual, both
the colour of the pigmented parent and of the pigmented ancestry
of the albino may appear among the individuals of the offspring.
Immediately subsequent to Cuenot, G. M. Allen in Ameriia
demonstrated the same Jact upon the same species of rodents.
C. C. Hurst, more recently, has shown that albino rabbits.
whether pure bred for eight generations at least, or extracted
from pigmented parents, may carry the determinants for black
or for black and grey. In this latter case the determinants
for black are carried by separate gametes from those carrying
grey, and the two kinds of sex-cells exist in approximately
equal numbers. This is likewise true of albino mice when
they carry the determinants for more than one colour.
Since Hurst's work, L. Doncaster and G. P. Mudge have both
shown that albino rats also carry in a latent condition
the determinants for black or grey. The experiments of the
latter author show that, if a gametically pure black rat be
crossed with an albino derived from a piebald black and white
ancestry, all the offspring in successive litters will be
black; but if the same black parent be crossed with albinoes
extracted from parents of which One or both are grey, then both
grey and black members will appear in the successive litters.
The proportions in which the various coloured individuals
appear are approximately those demanded by the Mendelian
principle of gametic purity and segregation. Cuenot and Hurst
have also shown that when albinoes of one colour extraction
are crossed with albinoes of another colour extraction the
segregation of the colour determinants in the gametogenesis
of the albinoes takes place in precisely the same way that it
does in the gametogenesis of a pigmented individual; that is,
in Mendelian fashion. Or, to express it otherwise, an albino
extracted from yellow parents, bred with an albino extracted
from black parents, will give an albino offspring whose
gametes in equal numbers are bearers of the black and yellow
determinants. And when one of these albinoes is bred with
a pure coloured individual, a mixed offspring will appear in
the first generation. Some of the individuals will be one
or other of the two colours, the determinants of which were
borne by the albino, and others the colour of the pigmented
parent. But in such albino crosses the colour characters
are latent because albinoes do not carry the whole of the
complements for colour production. They carry only some
determinant or determinants which are capable of developing
colour when they interact with some other determinant or
determinants carried alone by pigmented individuals. Whether
albinoes carry the tyrosinase or other ferment, or whether
they carry the chromogen or chromogens, is not yet settled.
Miss Durham's work suggests that they carry the latter. But
that they never bear both is proved by the fact that, when
albinoes are crossed with each other, none but albinoes ever
result in the offspring. One apparent exception to this rule
only is known, and this almost certainly was due to error.
It is not only among albino animals that colour factors
are carried in a latent condition, but also in white
flowers. W.. Bateson has shown this to be the case for the
sweet-pea (Lathyrus odoratus), var. Emily Henderson,
and for certain white and cream stocks (Matthiola.) When
white Emily Henderson (the race having round pollen grains)
is crossed with a blue-flowered pea, purple offspring
result. Similarly, when white Emily Henderson (long pollen
grains) is crossed with white Emily Henderson (round pollen
grains), the offspring wholly consists of the reversionary
purple type, and sometimes wholly of a red bicolor form known
as ``Painted Lady.'' These two types never appear in the same
family. With the stocks, when a white-flowered and hairless
form is crossed with a cream-flowered and hairless one, all
the offspring are purple and hairy. Bateson considers that
the purple colour is due to the simultaneous existence in
the plant of two colour factors which may be designated by
C and R. If either one of these two is absent the plant is
colourless. Cream-coloured flowers are regarded as white
because cream is due to yellow plastids and not to sap
colour. Thus the cream plant may carry C and the white
one R. When they are crossed the two factors for colour
production are brought together. Obviously, we may regard C
as a tyrosinase and R as a chromogen, or vice versa; and in
the case of the white sweetpea crossed with a blue-flowered
one, and producing purple offspring, we may imagine that
the white flower brought in an additional tyrosinase or a
chromogen not present in the blue flower, which, when combined
or mixed with the chromogen or tyrosinase for blue, gave
purple. A similar explanation may apply to C. Correns's
experiment, in which he crossed white Mirabilis jalapa with
a yellow form, and always obtained red-flowered offspring.
In heredity, complete albinism among animals is always
recessive; and partial albinism (piebald) is always recessive
to complete pigmentation (self-coloured). When an albino
mouse, rat, guinea-pig or rabbit is crossed with either
a pure self or pure pied-coloured form, the offspring are
similar to, though not always exactly like, the coloured
parent; provided, of course, that the albino is pure and
is not carrying some colour or pattern determinant which is
dominant to that of the coloured parent used. No albinoes,
in such a case, will appear among the first generation,
but if the individuals of this (F.1) generation are crossed
inter se or back crossed with the albino parenr, then
albino individuals reappear among the offspring. In the
former case they would form one-quarter of the individuals
of this second (F.2) generation, and in the latter, one-half.
The recessive nature of albinism and its distribution in
Mendelian fashion is almost certainly as true for man as
for lower forms. This has been shown by W. C. Farabee for
negroes in Coanoma county, Mississippi. The facts are as
follows. An albino negro married a normal negress. They had
three children, all males. All three sons married, and two
of them had only normal children, judged of course by somatic
characters. But the third son married twice, and by the
first wife had five normal and one albino children, and by
the second, six normal and three albino children. If we
assume that the two negresses which the third son married
were themselves carrying albinism recessive --an exceedingly
probable condition considering that albino negroes are not
uncommon---the result is accurately in accordance, as W. E.
Castle has shown, with Mendelian expectation. For there is
expected in the offspring of this third son coloured individuals
and albinoes in the proportion of 3:1. There is actually 11:4,
which is the nearest possible approximation with the number 15.
The operation of Mendelian processes in human heredity
is further shown by the close relationship that exists
between the appearance of albinoes and cousin marriages.
An albino is a homozygote; that is, all its gametes are
carrying the character of albinism and none of them bear the
alternative character --the allelomorph---of pigmentation. By
pigmentation is here meant all those factors which go to its
production. Now such a gametic (egg or sperm) constitution
can only result when two individuals, all or some of whose
gametes are pure with regard to the character albinism, meet in
fertilization. Hence it is readily seen that it is among
cousin marriages that the greater probabilities exist that
two individuals bearing identical characters will meet, than
in the population at large. This can be illustrated in the
following scheme. Let A stand for a pure albino and (A)N
for a normal person, who nevertheless carries the character
albinism (A) recessive. Then, in the scheme below, if Ab
and (A)Nb are two brothers who both marry normal wives
