94. It is possible, also, that other means may be at play in the promotion of such an effect (93) in the fœtus, besides the one before mentioned (91). We may instance as a probable one, lymphatic absorption. The probable existence of lymphatics in the placenta was admitted by Dr. Hunter. “It is most probable that it (the fœtus) is nourished by thousands of small lymphatic vessels which absorb nourishment from the blood of the mother and carry it along the navel-strings. It is true we cannot see any lymphatics running upon the navel-string, yet it is reasonable to conclude they do.”[[22]] Hunter’s conjecture has since been realized (Chaussier, Fohman, Uttini, Lauth). The second of these anatomists has delineated them in rich profusion, extending from the placenta along the funis, leaving the funis at the navel, and directing their course to the groin (Mayo).
95. Some have ascribed the nutrition of the fœtus to a regular deglutition and digestion of the amnionic fluid. Many facts render this opinion probable (Meckel). But there are also facts which would make nutrition by such a means impossible (Dr. Hunter). 1st. An embryo, at an early period, cannot be nourished by the mouth. 2dly. The amnionic fluid is mere water with a vestige only of albumen, the only nutritive quality in it. 3dly. A fœtus was seen whose intestine, a little below the duodenum, was impervious and divided through, and the lower end began at some distance from the higher portion. (Dr. Hunter’s MS. Lect.) 4thly. A full grown child was brought into the world without head, heart, lungs or intestines (Dr. Cooper, in Dr. Hunter’s MS. Lect.) 5thly. A kitten was sent to the Royal Society, full grown, born without either nose or mouth. (Dr. Hunter, ibid.) 6thly. I have the drawing of a pig (the preparation of which I exhibited at the Med. Ch. Soc. in 1814,) which was born, at the proper period, and full grown, without any vestige of the under jaw, and consequently without either mouth or any passage into the stomach.
96. Some have thought that the amnionic fluid was absorbed through the pores of the skin (Osiander), others through the mammæ of the fœtus (Oken). That the vesicula intestinalis (umbilicalis) contributes to the growth of the embryo is a great deal more probable (Blumenbach, Sœmmering, Lobstein, Joerg.) It is also not improbable that the gelatine of Wharton, contributes to that object (Lobstein). But these are all conjectures, for the probability or improbability of which as many arguments and real facts have been alleged on equally unquestionable authority. “Ce sujet,” observes Magendie, “a souvent exercé l’imagination des physiologistes, sans aucun profit réel pour la science.”
97. I am more inclined to believe in the existence of respiration in the fœtus as an additional means of facilitating growth and entertaining inherent life (Geoffroy St. Hilaire, Müller). The presence of air, analogous to atmospheric air, in the amnionic fluid, has been detected (Lassaigne). I once had in my possession an intact ovum at five months (30th June, 1826,) which served me for the purpose of studying more particularly the real structure of the placenta, and which contained, besides the amnionic fluid, a bubble of air about the size of a small plumb. Only a portion of this was, through the awkwardness of my assistant, received in a glass tube containing distilled water, while I punctured, under water, the membranes in the centre of the bubble. This portion was afterwards made to pass through a saturated solution of lime in water, and produced a visible cloudiness denoting the presence of carbonic acid. The respiration of the fœtus is supposed to be effected by the cutaneous pores, as in aquatic insects (Geoffroy St. Hilaire). In addition to which the placenta is looked upon as performing the office of lungs (Müller). Dr. Edwards’s experiments on the asphyxia of the Batraciens, may serve to throw light upon this question (Breschet).
98. The nature of the changes which the blood in the fœtus may be supposed to undergo from arterial to venous, and the converse, has not been satisfactorily ascertained. The colour of the blood in the umbilical vein is something lighter than that in the umbilical arteries (Mayo). This alleged change is not admitted by others (Meckel). I have never been able to detect the least difference between the arterio-umbilical and venous-umbilical blood, in the many cases I have examined. But the absence of any change of colour does not necessarily imply the absence of any inherent change in the blood of the two systems. The globules of the fœtal blood do not resemble those of the blood of the mother (Experiments alluded to by Dr. Breschet).
99. Connected with the subject of the nutrition of the fœtus and the changes which take place in the blood of it, may be mentioned certain recent discoveries[[23]], which would lead to the belief, that the function of the placenta is probably analogous to that of the liver during the intro-uterine life of the fœtus, and that the presence of bile in the blood of the placenta, discovered by modern chemists, is necessary to the maintenance of fœtal life (Breschet).
100. It is of the utmost importance to bear in mind the great distinction which exists between the independence of the fœtus, quoad life, and its dependence, quoad nutrition, in respect to the mother. The former state is secured by a total separation of the two circulations (maternal and fœtal). The latter by the close reciprocal contact of the organs of those circulations. Thence is it that we find the fœtus to live on, notwithstanding that its connection with the mother has been partially and sometimes even wholly, severed;—while on the other hand we cannot help admitting that, albeit this independence, the influence of the mother over the fabric of her offspring is unquestionable.
101. Here are two important positions. I have mentioned my experiments on the intact ova of the genus cat, (59,) to illustrate the first of them, and Dr. Prevost has since come to my assistance with as strong a case in further support of it[[24]]. This gentleman having observed an ovum still alive in the uterus of a ewe, which was a short time advanced in gestation, removed it and placed it upon a warm glass plate exposed to the rays of the sun, and attentively examined it with the microscope. The beatings of the heart became more lively. He noticed the blood arise to the surface of the chorion from the fœtus, there ramify plentifully, and by anastomosing vessels, return to two of the larger trunks which were the veins of the embryo. He concluded, therefore, that the ovum was an isolated substance.
102. In proof of the accuracy of the second position, we have equally strong evidence founded on experiments. Magendie introduced camphor into the veins of a pregnant bitch, and he found that the blood of the fœtus had, at the expiration of a quarter of an hour, acquired distinctly the smell of that drug (Physiology, 2d Edit. 1825). Quadrupeds carrying young were made to take with their food four ounces of madder-root. The colouring matter of that substance was found to have passed from the mother to the fœtus; as all the serum of the blood of the latter, the urine, the liquor amnii, the teeth and the bones were tinged with it (Dr. Mussy, 1829)[[25]]. In 1827, I undertook, at the request of Sir E. Home, a set of experiments on the human subject, with a view to ascertain the truth of my second position. Six gravid patients of one of the lying-in institutions under my direction, who required the constant use of aperient medicines, were instructed, towards the close of their time of gestation, to take at night, for a period which averaged about a week, from ten to fifteen grains of rhubarb in powder. After two or three days the effect was visible in the colour and smell of the urine of the patients previous to their confinement, and in one of them, in the colour and smell of the transpiration also. During the labour care was taken to preserve part of the amnionic fluid in a cup, the umbilical vessels were suffered to bleed on the side of the child after their recision, and the blood set apart so as to separate the serum, which was obtained in small quantity only.—Lastly, the first urine of the child was collected in sufficient portions. Each of these secretions appeared distinctly tinged by the yellow root, and bore the smell of it. When carbonate of magnesia was mixed with the fluids their colour became lateritious, and a reddish sediment was thrown down, evincing the presence of the drug which the mother had ingested. (MS. notes.)