FUNCTIONS OF THE FETUS.
Nutrition of the Rehm.
The nutrition of the fcetus passes through phases which correspond to the different epochs of foetal development.
Before the allantois is formed, the ovum derives its nourishment from the cells that form the discus proligerous; later it is sustained, through its first villosities, from the albuminous material enveloping it, and the liquid secretions of the uterine mucous membrane.
The embryo once formed, it is the umbilical vesicle which, with the aid of the omphalo-mesenteric vessels, furnishes the foetus with the materials necessary for its growth. But it is only when the allautois has conducted the umbilical vessels into the chorional villi and the placenta is formed, that foetal nutrition is definitely established. The placenta is the essential organ through which the foetus can draw from the maternal organism the elements necessary for its growth.
The theory that the amniotic fluid was swallowed and digested by the foetus has fallen back into the obscurity from which it ought never to have emerged, and all authors are in accord in viewing the placenta as the essential organ of foetal nutrition. But whilst the existence of utero placental vessels—of direct anastamoses between the maternal and foetal vessels—was admitted thirty years ago, modern authorities only have re cognized the peculiar structure of the chorional villi, and the absolute independence of the two circulations, and have sought for other explana tions.
Eschricht and Ercolani thought that the villi could draw the elements of nutrition from the uterine glands. Others have supposed that osmosis through the epithelial membranes that separate the two circulations explained the nutrition of the foetus; they confounded the respiration of the foetus with its nutrition.
Cl. Bernard, Zunz, Benicke. Zweifel, Fehling, and Gusserow have es pecially contributed to the elucidation of this problem. Bernard has called attention to the glycogenic function of the placenta. It is only a tem porary function; for as the liver is developed, the glycogenic material furnished by the placenta tends to diminish, until it almost entirely disappears during the last months of pregnancy.
Cl. Bernard, in demonstrating the existence of cellular elements whose function it is to elaborate the glycogenic material, has demonstrated by that fact alone, as Pinard claims, the passage of the elements constituting that material through the epithelial membranes of the villi.
But do all the materials pass ?—And under what forms do they do so? For experience teaches that while gaseous and liquid substances may thus pass, solids, no matter how finely subdivided, cannot do so. Hoffmann and Langerhans tried cinnabar, Jassinsky carmine, Fehling india ink, Davaine and Ballinger blood charged with bacteria, without being able to find any of these substances in the foetal blood. Ahlfeld was as unsuccessful with madder and indian ink, and showed that in pregnant bitches, fed exclusively upon fatty food, and whose blood was surcharged with fat—not a single fat globule could be found in the foetal blood.
On the other hand, Fehling proved that these same fatty substances in solution, together with proteid and mineral substances, could pass into the foetus. Benicke demonstrated the passage of salicylic acid, Gusserow of iodide of potassium and some liquid substances; Zweifel showed the passage of chloroform, and Fehling that of carbonic acid gas.
Singe then Thomas has tried morphine, Clouet phosphorus, de Lados arsenic, Constantin Paul and Baker lead, with success. It is demonstrated that the placenta is the essential nutritive organ of the foetus. But there is neither a digestion, properly so Balled, nor any absorption. The nutri tive principles are injected directly into the blood of the foetus.
Respiration of the Foetus.
Does the foetus respire ? Long a moot question, it is to-day decided that it does. There is, it is true, as Longet says, no respiration in the sense of adult respiration; but the interchange of gas, that takes place in the thickness of the placenta between the mother and child, constitutes a res piration as perfect as that of the full-grown being.