of Sex-Twins-The Rate of Growth-The Newb

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. T

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

gans, 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, ho

rom egg to offspring. By this means it has been definitely proved that the ovum multiplies rapidly after it has been fertilized, and becomes, as

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

out that time, too, the external sexual organs make their appearance. At first these are quite similar in both sexes; and, if th

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 w

t, 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 insect

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 t

proven, 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 possibilit

ch 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

with a surprising regularity for every 100 girls. Thus, the records of Berlin, Germany, for a hundred years show that the maximum difference occurred

"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

mewhat 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 lea

imately only one of ninety pregnancies, while triplets are extremely rare. It is true that even quintuplets may o

zation 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 remembe

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 calculat

h 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 cle

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 mo

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 u

ze 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 be

ether 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 chi

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 gro

re 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 a

y 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 bir

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

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; chan

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.

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, ma

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 organi

ina, 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 t

wo years of age. Infants of less than a year have been known to distinguish certain colored

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

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

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 i

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 ins

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 hum

itance. 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 albi

se 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 substanc

e 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,

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 thought

ngraves 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

gnancies 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 remembe

s 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 d

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 conceptio

nta; 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 nou

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; exce