THE EMBRYO
The Development of Form--The Determination of Sex--Twins--The Rate
of Growth--The Newborn Infant--Heredity--Maternal Impressions.
The new human being begins existence, as I have shown, as soon as the
ovum is fertilized, though at that moment it consists merely of a
solitary cell formed by the union of the two parental cells. From a
beginning relatively simple the human body develops into the most
complex of living structures; and, startling as it may appear to be,
it is demonstrably true that every one of the millions of cells which
compose an adult has descended from the ovum. Furthermore, the
individual himself is not the entire progeny of the ovum; the
placenta and the membranes dealt with in the preceding chapter, we
saw, were also derived from that same source. They possess only a
transitory importance, to be sure, and to most persons they are less
interesting than the embryo, yet we gave them consideration before
discussing its growth because the manner in which the ovum becomes
attached to the womb and draws nutriment from the mother primarily
determines the fate of a pregnancy.
Now that we have become familiar with the arrangements for the
protection of the embryo, we are prepared to learn how it develops,
and may accept the phrase, embryonic development, to cover the whole
period of existence within the womb. In a more technical sense,
however, the use of the term _embryo_ is limited to the first
six weeks of pregnancy and designates the condition of the young
creature before it has acquired the form and the organs of the
infant; after that time the unborn child is called a _fetus_.
Embryonic development, therefore, in the strictest sense of the term,
chiefly involves the shifting of various groups of cells and the
bestowal upon them of different kinds of activity. During this period
comparatively slight growth takes place. By about the twentieth week,
the house, it may be said, is set in order; and there follows a
period marked by the rapid growth of the fetus.
THE DEVELOPMENT OF FORM.--A very old explanation of embryonic
development was that the process consisted altogether in growth.
According to that view the embryo lay curled up in the egg; at the
outset it was equipped with organs, limbs, features, and all the
other bodily structures found in an adult. In order that the ovum
might be transformed into a mature infant, only unfolding and growth
were required. After the microscope came into use, however, so simple
an explanation could no longer be accepted. Scientists soon realized
that the embryo did not exist "ready made" in the ovum, which, even
when magnified, failed to bear the faintest likeness to a human
being.
Although the microscope made impossible this very simple explanation,
it gave in return a truer, if more complex, account of the
transformation from egg to offspring. By this means it has been
definitely proved that the ovum multiplies rapidly after it has been
fertilized, and becomes, as was explained in the preceding chapter, a
sac-like structure within which hangs a tiny clump of tissue. This
inner mass of cells forms the embryo.
It has proved a difficult task to secure very young human embryos,
and many of the ideas we hold relative to the initial stages in the
development of man are based upon what has been found true in certain
mammals, the class of animals to which we belong. The youngest human
ovum known at present has already undergone about two weeks'
development, and there the embryo is represented by a flat disk. From
this stage to the stage of complete development a satisfactory series
of embryos has now been collected, but it is impossible to give here,
even in outline, a description of the evolution of the human embryo.
No one can understand this intricate subject without the aid of
diagrams, models, and other material beyond the reach of all save
laboratory workers.
By the end of the second month the development of the embryo has
advanced so far that anyone could recognize its human shape. About
that time, too, the external sexual organs make their appearance. At
first these are quite similar in both sexes; and, if they are used as
the criterion, it is possible only toward the end of the third month
to say whether the embryo is a male or female.
THE DETERMINATION OF SEX.--The fact that a number of months pass
before the sex can be distinguished by an external examination of the
fetus has led to the erroneous belief that it can be influenced
during the early part of pregnancy or actually determined at will.
Various means to accomplish this have been suggested; many of them
depend upon modifying the mother's mode of living according as a boy
or girl is desired. The most widely known of these doctrines, that of
Schenck, was to the effect that the sex of the offspring is always
that of the weaker parent. He suggested, therefore, that increasing
the vigor of the mother by an appropriate diet would produce a male
child, whereas a decrease in her strength would lead to the opposite
result. His views, however, were incorrect. After studying extensive
statistics Newcomb came to the conclusion that "it is in the highest
degree unlikely that there is any way by which a parent can affect
the sex of his or her offspring."
Moreover, the results of experimental research clearly indicate that
we shall never possess the means by which a mother may control the
sex of her child. In the main laboratory investigations have sought
to answer two questions. First, at what time is the sex of the
offspring determined? and, second, what accounts for the origin of a
male in one instance and of a female in another? The study of these
problems has been carried on chiefly in connection with insects,
worms, and fowl; but as yet insurmountable difficulties have
prevented similar investigations in higher animals. For this reason,
it is not without the greatest caution that results thus far obtained
may be assumed to apply to man.
Sufficient facts, however, have been collected to admit no doubt
regarding the answer to the first question. In most animals it is
definitely known that the sex of the offspring has been fixed when
the male cell enters the female cell, in other words, at the instant
the ovum is fertilized. Excellent reasons exist for believing that
human beings conform to this rule, and that the sex of the child is
unalterably determined at the moment conception occurs. Consequently,
any attempt to influence it after that event must prove futile.
For the present, the second question cannot be answered with equal
assurance. More than five hundred theories have been offered to
explain the relation of sex; nearly all of them have no reasonable
foundation and are only of historical interest. The view that girls
are derived from the right ovary, boys from the left, has long since
been disproven, and deserves mention merely because the laity still
believe it. Happily, during the last few years, observations and
experiments have been made which greatly advance our knowledge of the
subject and give promise of an early solution of the problem. The
controlling factor in sex determination has been narrowed down to
three possibilities; it is inherited either from the single cell
contributed by the father or from the single cell contributed by the
mother, or it is determined by the effect these two cells have upon
each other at the moment when they unite. In most animal species the
weight of authority distinctly favors placing the whole
responsibility upon the male cell.
According to recent evidence, there are two kinds of male germinal
cells; one kind giving rise to female offspring and the other to
male. In all probability, at the time of the marital relation, these
varieties are deposited in the vagina in equal numbers; and,
moreover, the mode of their production is such as to place absolutely
beyond human control the possibility of changing this ratio. Since
only one spermatozoon enters the ovum, whether or not the child will
be a boy or a girl depends entirely upon which type gains entrance.
If this explanation is correct, and it is in accord with careful
biological observations, it removes from the mother all
responsibility for the sex of her child. Furthermore, since the facts
indicate that male-producing and female-producing spermatozoa are
present in equal numbers, it follows that practically there is an
even chance that an embryo will develop into a boy or a girl.
Birth statistics bear out this conclusion, as data gathered from many
countries indicate that when long periods of time are studied 105
boys are born with a surprising regularity for every 100 girls. Thus,
the records of Berlin, Germany, for a hundred years show that the
maximum difference occurred in 1820, when the males outnumbered the
females by 4.79 per cent.; the minimum difference, which was noted in
1835, was .64 per cent. in favor of boys.
No inquiry is more often submitted to the physician by prospective
mothers than this, "Can you tell me if my baby will be a boy or a
girl?" He cannot. Many rules, to be sure, have been advocated as safe
guides toward reaching the correct answer; every midwife possesses
her individual formula which she has "never known to fail." But the
boastful success depends upon the application of some such method as
the following, which I have heard my teacher, Dr. J. Whitridge
Williams, expose to his classes. The patient is asked if a boy or
girl is desired. She confesses, and is then informed that the sex of
her child will be the opposite of her wish. When this guess proves to
be correct, there is no doubt of the prophet's wisdom; when it is
not, his honor is protected, for the parents have had their hope
fulfilled. Their happiness makes them forgetful that the guess was
wrong, or, for that matter, that it was ever made.
It was once believed that the sexes might be distinguished before
birth by the number of heart beats occurring within a minute. In a
general way, the action of this organ in females is somewhat more
rapid than in males; and so it was thought that a rate of 144 or more
indicated the female and a rate of 124 or less the male sex. But
experience has taught that this rule leads to accurate prophecy in no
more than half of the cases. As a matter of fact, no means of
definitely foretelling the sex of the child has been discovered, and
I doubt if it ever can be.
TWINS.--As every one knows, pregnancy commonly terminates with the
birth of a single child. Twins appear in approximately only one of
ninety pregnancies, while triplets are extremely rare. It is true
that even quintuplets may occur, though up to 1904 only 29 authentic
instances could be collected from the whole range of medical
literature.
Twins are most frequently born to parents whose ancestors have
established this tendency; the trait is usually inherited from the
mother's family, though occasionally it is passed on through the
father. Of course, that does not explain the cause of twins, which in
reality may result from either of two circumstances. More commonly
their genesis depends upon the ripening of two eggs at about the same
time and the fertilization of both by two different spermatozoa. The
children, in this instance known as double ovum twins, may be of the
same sex or not. On the other hand, single ovum, or identical, twins
are always of the same sex; this follows, since but one egg and but
one spermatozoon are here concerned. The incident permitting twins to
develop from a solitary ovum must occur soon after conception has
taken place. It will be remembered that the first step in the
development of the fertilized ovum consists in its dividing into two
cells. Ordinarily, both these take part in the development of one
embryo, but occasionally they separate and give rise to two.
Frequently, the presence of twins can be recognized during the latter
months of pregnancy, and accurate means are known of determining
after they are born to which variety any given pair belongs.
THE RATE OF GROWTH.--When we recall the definite and often marked
differences in the physical character of women, such as weight and
height, it is surprising to learn that the prenatal development of
their children proceeds with uniform speed. One very practical result
is that the physician is thus enabled, at the birth of a premature
infant, to estimate accurately the period of its development. Various
criteria, some of which are easy of application, aid in this
determination. For example, the length of the child is practically
constant for each of the ten lunar months into which the whole
gestation period is divided; if, therefore, the length of the newborn
infant is known, the stage of its development can always be inferred.
From the fifth month the calculation is especially simple, since the
length measured in centimeters divided by the figure 5 gives the
month to which pregnancy has advanced. Similarly, we can infer the
period of development from the weight, though the calculation is more
intricate and the method less reliable, inasmuch as the size of the
child in the latter months varies somewhat according to the weight of
its mother.
At the end of the fifth month, the weight of the fetus is from nine
to ten ounces; whereas an average infant when born at the expiration
of the full term of pregnancy, that is, with the completion of the
tenth month, weighs about seven pounds. The fetus, therefore,
acquires roundly ninety per cent, of its weight during the second
half of pregnancy, which clearly indicates that Nature reserves this
period of gestation for the fetus to increase in size, a phenomenon
less mysterious but no less important than the evolution of the
embryo.
Nothing is more valuable than the weight in affording an indication
as to whether a prematurely born infant may be reared. It is unusual
to raise a child weighing less than four pounds, which corresponds
approximately to the end of the eighth lunar month of development (a
trifle more than the seventh calendar month). After this time, the
prospect of living becomes greater in proportion to the nearness with
which the infant has approached maturity. No truth exists in the
widespread belief that the seventh-month child is favored above that
born later but before the natural end of pregnancy. Experience has
taught that the probability of success in rearing the child increases
rapidly after the seventh month. This is reasonable on the following
somewhat theoretical grounds. The digestive organs later attain a
higher state of perfection, and are better prepared to carry on their
work satisfactorily. Moreover, the gradual deposition of fat beneath
the skin during the last two months of pregnancy materially assists
in fitting the child for the conditions met with in the external
world, since the fat affords a barrier against the escape of heat
generated within the body, making it much easier to keep the child's
temperature at the normal point. Even other more technical reasons
could be given to demonstrate the error of the superstition regarding
the seventh-month child--a conviction endorsed by medical men
hundreds of years ago and as yet not discarded by the laity.
When pregnancy has reached "term," the child, having completed its
prenatal development, is ready to cope with conditions as they exist
in the external world. At term the average child is twenty inches
long and weighs 7 1/7 pounds (3,250 grams). The length is remarkably
constant; but the weight, as is well known, is often somewhat above
or below the average figure. In a general way, smaller children occur
in the first than in subsequent pregnancies, and, moreover, may be
expected when the mother is a small woman, or poorly nourished, or
has worked hard during her pregnancy. On the other hand, a tendency
to bear large children is present when the opposite conditions
prevail. It is not unusual to see infants weighing eight or nine
pounds at birth, but babies of more than ten pounds are rare, and the
fabulous, though not infrequent, reports of fifteen and twenty-pound
infants are probably not based upon actual weighings, but upon the
impression of someone who has merely seen the child or perhaps
guessed the weight from lifting it.
Although the fetus frequently changes its position during the earlier
months of pregnancy, generally by the beginning of the tenth lunar
month it has assumed a permanent posture. It has then reached such a
size that it can best be accommodated in the cavity of the uterus if
its various parts are folded together so as to give the fetus an
ovoid shape. To secure this form its back is arched forward, and its
head bent so that its chin touches its chest; its arms are crossed
just below the head, its legs raised in front of the abdomen, and its
knees doubled up. In this form the fetus occupies the smallest
possible space.
With relation to the mother the position of the child, for several
weeks before birth, is one in which its long axis is parallel to the
long axis of her body. This remains true no matter whether the head
or the buttocks are to precede at the time of birth. In ninety-seven
out of a hundred cases, however, the head lies lowermost and
consequently is the first portion of the child to be born. The
opposite position, in which the head is the last portion born, is,
even with the most skillful treatment, somewhat more serious for the
infant, though not for the mother.
THE NEWBORN INFANT.--The baby at birth is not a miniature man. As
compared with an adult its head and abdomen are relatively large, its
chest relatively small; its limbs are short in proportion to the
body; and at first glance it appears to have no neck at all. The
middle point of a baby's length is situated about the level of the
navel, whereas in a man the legs alone represent approximately half
his height. The changes after birth consist chiefly in growth; but
not altogether, since at least one organ, the thymus gland, becomes
smaller and completely disappears during childhood, and other organs,
especially the liver, are proportionately smaller in the adult than
in the infant.
The body of the infant also differs from that of the man in
possessing greater softness and flexibility. These qualities depend
upon the nature of its skeleton, which is composed of more bones than
later in life, when several have fused together to form one to give
the mature body a more rigid frame. Furthermore, the individual bones
are not so firm, consisting of an elastic material called cartilage,
so that some movements which in an adult would cause such serious
injuries as fractures and dislocations are perfectly harmless to a
newborn child.
The legs are not only short in proportion to the body but are always
curved, and the feet are held with the soles directed toward one
another, a position clearly abnormal in the adult. But every mother
should know that these are natural conditions in the infant, and are
the result of the posture of the child before birth. They soon
straighten out. The bowed legs of an adult are of an entirely
different origin, resulting from a disturbance of nutrition in
infancy called rickets.
A small amount of short wooly hair is usually found over the back of
a newborn infant. More conspicuous, however, is the presence there of
a gray, fatty substance which, though always more abundant over the
back, is at times distributed over the whole body; rarely is it
entirely absent. The material, technically named the vernix, is the
product of the glands in the skin and is a perfectly normal
secretion. After its removal, which is readily accomplished by
greasing the infant with lard or vaselin before giving the initial
bath, it never reappears.
A varying amount of hair covers the head of the infant. No
significance should be attached to the quantity, for the conviction
that exists, especially among negroes, that a heavy suit of hair for
the child occasions "heart-burn" in the mother during pregnancy is
without foundation. The color of the hair at birth does not indicate
its ultimate shade; changes are often noted during infancy. Similarly
the permanent color of the eyes is not assumed until later; at the
time of birth the eyes are generally, if not always, blue in color.
A baby's head is a matter of great concern to the family.
Occasionally, the skull is round and well shaped from the moment of
birth, but more often it is long and narrow; sometimes the form is
even startling to the inexperienced. The peculiar shape of the head
results, of course, from its passage through the birth-canal and is
not a sign of any disease. In a few weeks, or even less, the strange
appearance passes away. It is unwise to attempt to alter the shape of
the head by bandaging or massaging since the growth of the brain will
spontaneously accomplish what is desired; interference can do no
good, and may do serious harm.
Nature facilitates an appropriate molding of the head during birth so
as to permit its easy passage through the bony pelvic cavity of the
mother, and gains that end in two ways. The bones of the head remain
pliable until after the infant is born, and, further, their edges are
not welded together as in an adult, but are separated from one
another by an appreciable distance. During the act of birth the edges
are brought into contact or even overlap, materially reducing the
size of the head. Within a few hours after birth the bones again
spread apart, and some months elapse before they begin to unite; the
union is not completed until some time during the second year of
infancy.
Many mothers are anxious to know how far the senses of the infant
have developed when it enters the world. This problem has stimulated
some scientific investigation, though hardly so much as its interest
would justify. Two lines of inquiry have been pursued toward its
solution. The objective point of one of these has been to determine
how nearly the sense organs of the newborn correspond anatomically to
those of an adult; that is how perfectly has their organization been
completed. The other has been to learn how the infant reacts when the
various senses are stimulated; the interpretation of these reactions
is, however, particularly liable to error and sometimes amounts only
to guesswork.
The organization of the nerves and muscles in the eye is far from
perfect at the time of birth. The muscles act irregularly; indeed,
the lack of muscular adjustment is such that movements of the eye
likely to alarm the parents are regularly observed in very young
infants. Furthermore they cannot focus images which fall upon their
eyes. The retina, which receives visual impressions, has reached such
development at birth, however, that sensations of light can be
perceived. For example, if a lamp is suddenly flashed before the face
of a newly born baby it cries. From this and similar evidence,
indicating that strong light irritates the delicate structures of the
eye, we have learned that a nursery should not be illuminated, during
the day or night, so brightly as the rooms adults occupy. Certainly
several weeks, and probably several months, pass before an infant can
see anything save as blurs of light and darkness. Objects, such as a
hand, probably appear as shadows, which are not correctly interpreted
until late in infancy.
In regard to color vision we have as yet no reliable information
concerning children under two years of age. Infants of less than a
year have been known to distinguish certain colored papers. But such
discrimination is probably due to a difference in brightness of the
colors.
Although the organ of hearing is well developed at birth, the drum of
the ear in very young infants cannot transmit sounds, as in the
adult. For the latter kind of transmission it is necessary that the
pressure on both sides of the drum-membrane should be equal, and this
is arranged by the admission of air to the middle ear through a
passage from the throat. At the time of birth, on account of the
swollen condition of the mucous membrane which lines this passage, it
is blocked, and the middle ear is filled with fluid; these conditions
interfere with the transmission of sound, and consequently its
perception is dulled. But even in the absence of a drum-membrane an
adult can hear; the vibrations in such cases are transmitted through
the bones of the skull, and this very likely also occurs in newly
born infants. In most instances, at least, they react to a
disagreeable noise within the first twenty-four hours, and their
sensitiveness in this direction explains why the nursery should be
kept quiet.
Investigators have not come to uniform conclusions concerning the
sense of smell and of taste. In all likelihood, smell is not acute at
the time of birth. Taste probably is better perceived, yet some
newborn babies are said to suck a two per cent solution of quinin as
eagerly as milk, though stronger solutions are distasteful. According
to the best available information a young infant can detect the
difference between a sweet, bitter, sour, or salty taste only when
the tests are made with a solution possessing the quality in question
to a marked degree. It is common knowledge that babies cheerfully
suck the most tasteless objects, and it is not improbable that at
first the reaction depends upon the temperature of the object and the
feeling it creates in the mouth.
The moment it is born, a baby perceives pressure if its skin is
touched. To this sensation, however, some parts of the body are much
more sensitive than others; the tongue and lips are most sensitive of
all. Heat and cold are probably perceived more acutely by infants
than by adults; to pain, on the other hand, babies are less
sensitive. An infant is aware of the movements of its own muscles,
and also appreciates a change from one position to another, as
experienced nurses know very well, and on that account carefully
avoid keeping a baby on one side continuously.
The vast majority of movements performed by young infants are reflex
acts, that is, the cerebrum, the part of the brain with which
thinking is done, is not concerned with their performance. Of these
reflexes the most notable are sucking and swallowing, but sneezing,
coughing, choking, and hiccoughing may also be observed; stretching
and yawning have been recorded in several instances, even during the
first days of infant life. None of these movements, we must remember,
are produced consciously; the baby cannot reason and does not
recognize anyone, even its mother.
HEREDITY.--The transmission of bodily resemblance and of traits of
character from parent to child is a broad and complicated subject,
whose fundamental principles biologists are just beginning to grasp.
The facts thus far established regarding heredity relate chiefly to
plants and to the lower animals. There is no doubt whatever that the
meager knowledge we possess of heredity in man will be amplified and
will ultimately indicate on the one hand the marriages which are
advisable and, on the other hand, those which are not. Indeed, the
foundations for a science called Eugenics, which purposes to improve
the human race in this way, have already been laid. It is barely a
decade, however, since our knowledge of heredity has approached that
order and system which entitle it to be ranked as a science; and in
this brief period great strides could hardly be expected in its most
intricate field, that of human inheritance.
The modern teachings of heredity are of interest to us, nevertheless,
since they intimate the time when a child's inheritance is fixed and
the means by which hereditary characters are conveyed. To understand
these fundamental points we must recall that at the moment of
conception a male germinal cell combines with a female cell, and that
this act, which is named fertilization, brings together vital
elements from the two parents. We have seen that the spermatozoon
represents the solitary contribution of the father toward the
development of the child, and the spermatozoon, therefore, must
convey the material basis of paternal inheritance. Similarly we might
expect the ovum to be the bearer of the maternal qualities inherited
by the child. This is actually true; but much of the evidence is of a
technical character and must be omitted. Yet an experiment
successfully conducted by Castle and Phillips will indicate, even to
those who have no special knowledge of the mechanism of heredity, the
important role the ovum plays. These investigators removed the
ovaries from an albino guinea-pig, and in their place substituted the
ovaries of a black guinea-pig. "From numerous experiments it may be
emphatically stated that normal albinos mated together produce only
albinos." But in this experiment the result was otherwise, for the
albino into which the ovaries of a black guinea-pig were grafted
produced only black offspring. The color-coat of her young,
therefore, was not influenced by her own white hair, but was
determined by the eggs really belonging to the black animal from
which the ovaries were taken; in no other way can the result be
interpreted. It is certain, moreover, that the mode of transmission
of material qualities here exemplified is not exceptional; on the
contrary there is no doubt that the ovum always conveys the sum total
of the qualities the offspring inherits from the mother.
The germinal cells then contain the material basis of inheritance,
and in all probability the substance is located within the nucleus of
the cells. This substance had been seen and studied long before its
relation to the problem of heredity was suspected. Because it takes a
deeper stain than the rest of the nucleus, it stands out prominently
when the cell is treated with certain dyes, and this property
accounts for its name--chromatin. Under such conditions as prevail
just before a cell divides, the chromatic substance is broken up and
reassembled in the form of rods called chromosomes. Curiously enough
the number of rods is uniform for each species of animal, though
different numbers are characteristic of different species; the
characteristic number for man is twenty-four.
Unless some arrangement was made to prevent it, the act of
fertilization would cause the number of chromosomes in the fertilized
ovum to be double the number characteristic of the species. In man,
for example, the addition of twenty-four chromosomes from the
spermatozoon to an ovum that already contained twenty-four
chromosomes of its own would mean that after fertilization the ovum
contained forty-eight. Such a result is prevented through the process
to which we have referred in the preceding chapter as the ripening of
the ovum, and also through a similar process in the case of the
spermatozoon. These two processes lead to a reduction in the number
of chromosomes, so that finally every human germinal cell contains
twelve, and therefore when the ovum is fertilized the characteristic
number twenty-four is restored. While we know nothing of the forces
which determine, on the one hand, what elements shall be discarded by
the germinal cells and, on the other hand, what elements shall
remain, it is definitely proved that a selective process always takes
place. This fact admirably explains the variation in the
characteristics inherited by children of the same family. So far as
is known, the traits which will be passed on from either parent are a
matter of chance. Whatever these hereditary traits happen to be, the
best evidence we have indicates that the problem of a child's
inheritance is settled once for all the moment conception takes
place.
MATERNAL IMPRESSIONS.--Contrary to all that we know of heredity, the
conviction prevails among the laity that the character of a child
depends greatly upon the mother's surroundings during pregnancy: this
is the doctrine of maternal impressions. As is usual with
superstitions, this one emphasizes the unfavorable possibilities and
holds that the unborn child may be affected by the mother's unhappy
thoughts or maimed by her mental distress if she is exposed to
unpleasant sights. For this belief there is no foundation; the cases
often cited in its support may be fully explained on the grounds of
coincidence.
With the possible exception of such individuals as are spending their
lives in solitary confinement, there is scarcely a human being who
has not in the course of nine consecutive months some untoward
physical or mental experience which engraves itself upon the memory.
Prospective mothers are not apt to be exempt from a rule so general
in its application, but if by good chance one happens so to be she
will hardly fail to hear of the misfortune of others, which,
according to the doctrine of maternal impressions, may be equally
effective in interfering with the proper development of the child. We
should then rightly expect most, if not all, babies to be "marked"--
clearly a situation which does not prevail.
In order to learn how frequently prospective mothers may have
disagreeable experiences which they fear will affect the formation of
the child, I have lately asked the patients whom I have attended,
"Was there any incident during your pregnancy to which you could have
attributed the infant's condition, had it been marked?" The babies of
all those to whom the question was submitted were normal; yet without
exception those whose pregnancies just completed were their first
answered in the affirmative. It is also pertinent that one of these
patients had lost her brother by a violent and accidental death when
she was four months pregnant; a similar bereavement was suffered by
another at the eighth month; each was, however, delivered of a
perfectly healthy child. Among those with whom the recently ended
pregnancy was not the first I found some who could remember incidents
popularly believed to have an influence over the development of the
embryo; most of them, however, had given the matter so little thought
that they could not definitely recall whether such incidents had
occurred or not. From a similar series of observations covering two
thousand cases, William Hunter came to the conclusion, nearly two
hundred years ago, that there was no support for the belief in
maternal impressions.
Whenever a child does happen to develop abnormally, it must be clear
that, from the very nature of our existence, some incident can be
recalled which will satisfactorily, yet unjustly, bear the blame. It
may be confidently said, however, that, for every mother whose fears
are realized, hundreds are agreeably disappointed in finding their
babies perfectly normal. In the face of so many negative instances it
is amazing that any person, even though ignorant of medical teaching,
should be inclined to attribute abnormal development to something the
mother has seen or heard, thought or dreamt, or otherwise experienced
while she was pregnant. Yet unfortunately many do believe this. It is
worth while, therefore, to supply further evidence, and thus escape
any suspicion of unfairness in argument, to prove that maternal
impressions are unable to affect the formation of the embryo.
It is found, as a matter of experience, that the superstition
regarding maternal impressions generally begins to cause anxiety
during the second half of pregnancy; and then such an influence is
entirely out of the question. By the end of the second month the form
of the embryo has been definitely determined, and subsequently cannot
be altered. It is even true that errors in development are most apt
to occur within the two or three weeks that immediately follow
conception, and therefore occur at a time when pregnancy is not often
clearly recognized. Thus it happens that women begin to worry about
the influence their minds will have upon the formation of the child
long after its form has been established.
Incidents in the life of a prospective mother are in point of fact
equally inert so far as their influence upon development is
concerned, no matter whether they occur during the earlier or later
part of pregnancy. There is never any anatomical means by which
maternal impressions could be conveyed to the embryo. Such an
influence would have to be exerted through the placenta; and that is
impossible. There are no nerves in the placenta to carry impulses
from the mother to the child. Even the blood streams of the two
beings are kept apart; and though it is unheard of that the blood
should carry nerve impulses, if that happened to be the case, it
could not prove effective here, for the blood of the mother does not
enter the child. It is nourished by food which passes from the
mother's blood, to be sure, but there is no more reason to expect
this nutriment to exert an hereditary influence than there is to
expect an infant to grow to resemble the cow with the milk of which
it is fed. With these two possibilities eliminated, no path can be
imagined by which impulses might travel from the mother to the
embryo.
Scientific investigation has brought to light these facts, as it has
also taught the real causation of the disfigurement once attributed
to the mother's mind. Departures from the usual form of the body
occur during the earliest days of pregnancy and arise in consequence
of some irregularity in the process which molds the body-form from a
simple spherical mass of cells. Why irregularities sometimes occur is
not altogether clear; except in so far as it has been determined that
the fault lies within the embryo itself. Whenever these defects are
associated with events which have disturbed the mother's mind, it
cannot be other than a simple coincidence.