A positive proof that the nutrition is supplied by means of the cord, and in no other way, is found in the well-known fact that compression of the cord so as to arrest the circulation, although but for a very short space of time, is certain death to the child. What change the nutritious material obtained from the mother undergoes before it is fitted for appropriation by the foetus, or where that preparatory change is made, whether in the foetal or in the foetal liver, is not yet known. Nor is it known where or how the plant transforms the nutriment derived from the earth, into its peculiar sap, fibre and bark.
RESPIRATION.- This function is essential to the essential to the existence of all the animals of creation; and for every individual thereof. For this is the process by which the effete blood becomes aerated, and gives up the excess of carbon and other morbid matters with which it is loaded. This, as just above described, is accomplished by the foetal blood coming in contact with the maternal, through the vascular coats of their respective blood-vessels, in a manner not unlike that in which the blood of fishes is decarbonized be being exposed, by means of the gills, to the air contained in the water which passes through them. The blood of the mother serves exactly the same purpose for that of the foetus, that the water does for the blood of fishes; the water contains an appreciable amount of air or rather of oxygen; and so does the mother’s blood. In proof of this, it is only necessary to compress the cord so as to prevent the blood of the foetus from being exposed to that of the mother, and the child black and dies, as from asphyxia.
SECRETION.- As development advances, all the secretions are successively established. The liver secretes bile, the gall- bladder is found full; and there is reason to believe that it is steadily supplied to the intestines. Even prior to the fifth month, the alimentary canal contains a substances called meconium, which is principally composed of biliary matter and the detritus of the mucous membrane. There is no positive evidence that his meconium is ever evacuated into the amniotic sac; but it sometimes passes off freely during labor; and in other cases no long after delivery. This is secreted, and usually passes in considerably quantities after birth, and it is thought by some that the foetus in utero discharges the urine into the amniotic cavity. But we have no positive evidence that the is ever discharged from the bladder till after delivery.
CIRCULATION.- In the foetal circulation there are apparently different streams of blood, and consequently the circulation is here more complicated than in the child after birth. The blood returned from the placenta, richly laden with the nutritious elements from the mother, enters the ascending vena cava, either directly or indirectly through the liver; passes through the right auricle of its heart into the left auricle; thence in to the left ventricle; and from thence it is made to ascend the aorta to supply the head and upper part of the body; it then passes into the veins, and descends into the descending vena cava, and through a foramen, called the foramen of Betel, into the right ventricle; then through the ductus arteriosus into the aorta to descend into the lower part of the body, a portion returning through the iliacs to the mother to be replenished and again returned to the embryo as before.
The ventricles, in the foetus, act in unison, when one contracts the other does. Thus when they contract, their respective streams of blood meet in the aorta, one from the left ventricle, the other from the ductus arteriosus; so that one acts as a dam to the other. Consequently, the stream from the left ventricle, being uppermost, is made to ascend by the stream coming in from the right ventricle at the same time just below; this latter of course descends the aorta. Thus the extremes os the foetal circulation meet to be separated by extremes, to meet again.
Immediately after birth, the lungs being opened to the circulation, for the purpose of aerations, the blood takes new channels more easily than it can follow the old ones; and the whole circulation becomes more simple. All the blood entering the right auricle is thrown at once into the right ventricle, and from thence with great ease into the pulmonic artery to be distributed to the lungs for aeration. From the lungs it is returned by the pulmonic vein to the left auricle, thence into the left ventricle, to be again distributed by the ascending and descending aortas to the whole system. All other passages in the lungs are of course thus close up, from want of use. And in iliacs which formerly carried a portion of the blood to the mother in search of the materials for renovating and revivifying it, now receive supplies through the mouth and alimentary canal of the child.
MULTIPLE PREGNANCY.- It is by no means an uncommon occurrence for a mother to give birth to twins. From very extensive observation this has been noticed to occur about once in seventy- five cases. Triplets occur still less frequently; say one in six thousand cases; while quadruple pregnancies are rarer still. The cause of the anomaly of multiple pregnancy may arise from there being two or more yolks in the same egg, two or more eggs in the same vesicle, or two or more ovules in separate vesicles, or one or more ovules may be at the same time impregnated in each ovary. In these respects there seem to be no end to anomalies and strange varieties. Nature seems disposed at times to imitate in man the wonderful fecundity of the lower orders of creation.
Multiple pregnancies can only be positively determined by clearly and unmistakably distinguishing the beat of more than one foetal heart. In this class of pregnancies one embryo or more may perish, dry up as it were, leaving the remaining one to be developed in a fine healthy condition to full term. After the birth of the living, the head will also be discharged. The membranes are differently disposed in different multiple pregnancies. Each child may have its own separate membranes and placenta; or there may be one placenta and two cords; each a separate amnion, but all enveloped in the chorion. Or again, two foetuses may be found in one amnion, and enveloped in a single chorion. Sometimes also the body of one foetus is found inclosed within that of another; this is called a monstrosity by inclusion.
EXTRA-UTERINE PREGNANCY.- Impregnation is effected within the ovary, as described in a previous chapter. (*This does not accord with the views of some modern physiologists, who affirm (Dalton’s physiology, chap. vii.) that “the egg comes in contact, after leaving the ovary, and while passing through the Fallopian tube, with the spermatic fluid, and is thereby fecundated. “The spermatic fluid meets the egg at or soon after its discharge from the ovary, p. 562. (vide et 574.) Muller, on the contrary, teaches that “the ovary is the place of impregnation, at all events, in man and mammiferous animals. Elements, ii., p. 1491.) But where the fecundated ovule fails to reach the cavity of the uterus, it may lodge, adhere and become developed in some other place; this constitutes extra-uterine pregnancy.
Sometimes the impregnated ovule remains in the ovary, and is there developed, constituting ovarian pregnancy. The autopsy of a woman suddenly dying has revealed, as the cause of her dissolution, an enlarged ovary rent in twain by a foetus of four and a half months. The ovary could no longer accommodate the foetus! Sometimes the ovule is arrested in its progress down the Fallopian tube, attaches itself to its walls, and proceeds to develop itself as a new human being; this is called tubal extra- uterine pregnancy. In other instances, on account of some abnormality of structure, the ovule slips in between the interstices of the uterine walls, and develops there in what is termed utero-interstitial pregnancy. The ovule in some cases remains fixed between the fimbriated extremity and the ovary; this results in ovaro-tubal extra-uterine pregnancy. And in those instances in which it drops down into the cavity of the abdomen and fastens and develops itself upon some portion of the serous membrane, or peritoneum, it constitutes what it called abdominal extra-uterine pregnancy.
The made of development in these abnormal cases is precisely similar to that in others. Internally the ovule goes on developing precisely as in normal pregnancies, in the formation of the amnion, chorion, umbilical cord, &c. Externally, to whatever point the ovule may become attached, it becomes so attached by means of the villi of the chorion growing into whatever structure they are brought into contact with. Simultaneously with this growth on the part of the ovule, the maternal structure grows to correspond and to furnish her part in the reproduction, by growing upon these villi and throwing out blood-vessels to meet those coming from the embryo. Thus the placenta is formed precisely in a similar manner here as in the uterine cavity,- only with far less present security to the embryo, and with almost certain fatal consequences to the mother.
