Zweifel has shown that this idea of foetal respiration is indicated in the hippocratic books;—but that authorities were divided into two camps, one of which considered the placenta to be a real foetal lung, and the other claiming a pulmonary respiration like the bronchial respiration for the foetus, it being supposed to receive its supply of air from the liquor amnii. The discovery of oxygen by Lavoisier, and the realization of its important role in respiration, seemed to throw light upon the question. But while Clark and Darwin proved that in the egg of the chicken during incubation the venous differed from the arterial blood in color, while Bohn in dogs and Hoboken in the human foetus showed that the blood of the umbilical vein is bright red, and the blood of the umbilical arteries reddish purple, thus confirming the statements of Scheel in 1799, Schutz, Autenreith and Bichat declared that they had never been able to appre ciate such a difference.
Muller began by accepting the theory of a foetal respiration—though he held it to be much feebler than that of the new-born; but he soon rejected it, and, confounding respiration with nutrition, claimed that the necessary juices passed directly from the maternal vessels into the foetal blood.
Bischoff rejected the theory of a placental respiration. The placenta he held to be a maternal organ. The foetus had no proper animal heat— and neither had it any proper respiration.
But a reaction soon came, and Litzman, returning to the idea of a placental respiration, regarded the placenta as a true respiratory organ. The oxygen of the placenta was not consumed by that organ, but was in great part transmitted directly to the foetus Through the umbilical vein.
Schutz and Autenreith, experimenting with the foetus of the rabbit, found its temperature, immediately after leaving the uterus, to be three degrees Ittamur (39° F.) less than that of the mother, whilst Barensprung claimed that it may be the same, or more or less so, as the temperature of the maternal passages.
Wurster, under Gusserow's direction, was able to prove that the fcetns in man possessed a proper animal heat of its own, since he found it in breech cases to' be higher in the foetal rectum than in the maternal genitals.
Schwartz considered respiration proven from the presence of urea and uric acid in the foetal urine; while Schultz noticed that the foetus begins to make energetic attempts at respiration, whether within or without the uterine cavity, as soon as the utero-placental circulation is interrupted.
Finally, Levallais showed that the respiratory centre is situated in the medulla oblongata, and Volkmann proved that the respiratory excitability depends upon the venousness of The blood.
Thus there occurs in the placenta an interchange of gases analogous to that which occurs in the lungs of the new-born child, and which prevents the foetus from making inspiratory attempts. In a word, the fcetus re mains apnceic because, the placenta functionating regularly, its blood never becomes venous enough to excite the special respiratory centre. The foetal blood and the maternal blood are only separated by the walls of capillaries; they are in mediate contact. On both sides this blood is in active circulation; and since the maternal blood is always saturated with oxygen, the foetal blood must possess an equivalent quantity. But the
combustion processes are not intense enough in the foetus to make the foetal respiration very energetic. And from this small intensity of respi ration and small expenditure of oxygen arises the marked resistance to asphyxia displayed by the fatal organism.
Schroeder, accepting these ideas, has proved that the bodies of foetuses that succumb to an interruption of the placental circulation, show all the signs of death by asphyxia or by drowning.
Zweifel, following in the line of Iloppe-Seyler's researches, has shown, by the spectroscope, that oxyhtemoglobin exists in the umbilical vessels of the foetus, and that the absorption bands of oxyhtemoglobin are very distinct even in cases where the cord had been tied during delivery and before the first festal respiration. Since, therefore, before delivery the only possible contact with oxygen is at the placenta in the maternal blood, Zweifel has given direct proof of the passage of oxygen from the maternal to the festal blood, and through the epithelium of the chorionic Zweifel then began a series of experiments upon pregnant rabbits, which were tracheotomised, and provided with a canula and means of artificial respiration. After anaesthetization, laparatomy was done and the uterus opened, while the entire body of the animal was submerged in a , 0 saline solution kept at an even temperature of 38°. He found, in every case, that asphyxia upon the part of the mother caused the blood in the umbilical vein to become as dark as that in the arteries, and that the fcetus then made attempts at inspiration. On doing artificial respiration to the mother the vein regained its normal color, and the festal respiratory attempts ceased. Zweifel therefore concluded that the fcetus respires through the placenta, and that this placental respiration is subject to the same conditions as is the respiration of the child after birt/h.
Thus the fcetus, by means of the placenta, absorbs oxygen and gives up carbonic acid. But, contained as it is within the body of the mother, it is not exposed like the infant to any considerable loss of heat, and hence needs very much less oxygen.
A fact that proves how little oxygen is really necessary for the fcetus, is its resistance to asphyxia, which we mentioned above, and which, as Tarnier and Chantreuil remark, varies with the individual and probably with certain conditions still unknown to us. " Thus, when the mother dies of simple asphyxia, the fetus dies easily, not only because the fetal blood does not receive the oxygen from the maternal blood, but because the latter takes from the festal blood the oxygen that does not come to it by the respiratory passages. The rapidity of the death of the fetus depends therefore on the rapidity with which it gives up its oxygen to the mother, and this depends probably upon the composition of the maternal blood. If, for example, the mother has been asphyxiated by the fumes of charcoal, her blood will contain an amount of carbon dioxide which will render her blood globules unfit for the absorption of oxygen; and the maternal blood will take so little oxygen away from the fetal blood, that the death of the foetus will take place very slowly. Such, at least, would appear to bo the conclusions to be drawn from the curious experiments of Andreas Htigyes and Zunz." (Tarnier and Chantreuil).