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Page 50
In certain cases the inheritance is transmitted by the female alone.
This is the case in the h�mophilia, the unfortunate subjects of which
are known as bleeders. There is in this a marked tendency to
h�morrhage which depends upon an alteration in the character of the
blood which prevents clotting. This, the natural means of stopping
bleeding from small wounds, being in abeyance, fatal h�morrhage may
result from pulling a tooth or from an insignificant wound. There is a
seeming injustice in the inheritance, for the females do not suffer
from the disease although they transmit it, while the males who have
the disease cannot even create additional sympathy by transmitting it.
The most obvious inheritance is seen in the case of malformations.
These represent wide departures from the type of the species as
represented in the form. There is no hard and fast line separating the
slight departures from the normal type known as variations and
mutations, from the malformations. Certain of the malformations known
as monstrosities hardly represent the human type. These are the cases
in which the foetus is represented in a formless mass of tissue, or
there is absence of development of important parts such as the nervous
system or there is more or less extensive duplication of the body.
There has always been a great deal of popular interest attached to the
malformations owing to the part which maternal impressions are
supposed to play in their production. In this, some striking
impression made on the pregnant woman is supposed to affect in a
definite way the structure of the child. The cases, for instance, in
which a woman sees an accident involving a wound or a loss of an arm
and the child at birth shows a malformation involving the same part.
There is no association between maternal impressions and
malformations, although there have been many striking coincidences.
All malformations arise during the first six weeks of pregnancy known
as the embryonic period, in which the development of the form of the
child is taking place, and during which time there is little
consciousness of pregnancy. Maternal impressions are usually received
at a later period, when the form of the child is complete and it is
merely growing. It must be remembered also that there is neither
nervous nor vascular connection between the child in the uterus and
the mother, the child being from the period of conception an
independent entity to which the mother gives nutriment merely. Of
course, as has been said, the mother may transmit to the child
substances which are injurious, and in certain cases parasites may
pass from the mother to the foetus. The same types of malformations
which occur in man are also seen in birds, and it would require a more
vigorous imagination than is usual to believe that a brooding hen
could transmit an impression to an egg and that a headless chick could
result from witnessing the sacrifice of an associate. The idea of the
importance of maternal impressions in influencing the character of the
offspring is a very old one, a well-known instance being the sharp
practice of Jacob's using peeled wands to influence the color of his
cattle. In regard to coincidences the great number of cases in which
strong impressions made on the mind of the pregnant mother without
result on the offspring are forgotten. The belief has been productive
of great anxiety and even unhappiness during a period which is
necessarily a trying one, and should be dismissed as being both
theoretically impossible and unsupported by fact.
The malformations are divided anatomically into those characterized,
first, by excess formation, second, by deficient formation, third, by
abnormal displacement of parts. They are due to intrinsic causes which
are in the germ, and which may be due to some unusual conditions in
either the male or female germ cell or an imperfect commingling of the
germinal material, and to extrinsic causes which physically, as in the
nature of a shock or chemically as by the action of a poison, may
affect the embryo through the mother. Malformations are made more
numerous in chickens by shaking the eggs before brooding. A number of
malformations are produced by accidental conditions arising in the
environment; for instance, the vascular cord connecting mother and
child may become wound around parts constricting them or even cutting
them off, and the membrane around the child may become adherent to
certain parts and prevent the development of these. The extrinsic
causes are more operative the more unfavorable is the environment of
the mother. Malformations are more common in illegitimate children
than in legitimate and more common in alcoholic mothers; there is an
unfavorable environment of poverty in both cases, added to in the
latter and usually in the former by the injurious action of the
alcohol.
The more extensive malformations have no effect on heredity, because
the subjects of them are incapable of procreation. The malformations
which arise from the accidents of pregnancy and which are compatible
with a perfectly normal germ are in the nature of acquired
characteristics and are not inherited. Those malformations, however,
which are due to qualities in the germinal material itself are
inherited, and certain of them with remarkable persistence. There are
instances in which the slight malformation consisting in an excess of
fingers or toes has persisted through many generations. It may
occasionally lapse in a generation to reappear later. In certain
cases, notably in the bleeders, the inheritance is transmitted by the
female alone, in other cases by the sexes equally, but there are no
cases of transmission by the male line only. It is evident that when
the same malformation affects both the male and the female line the
hereditary influence is much stronger. A case has been related to me
in which most of the inhabitants in a remote mountain valley in
Virginia where there has been much intermarriage have one of the
joints of the fingers missing. There is a very prevalent idea that in
close intermarriage in families variations and malformations often
unfortunate for the individual are more common. All experimental
evidence obtained by interbreeding of animals shows that close
interbreeding is not productive of variation, but that variations
existing in the breed become accentuated. Variations either
advantageous or disadvantageous for the race or individual may either
of them become more prevalent by close intermarriage. It seems,
however, to have been shown by the customs of the human race that very
close intermarriage is disadvantageous.
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