with its peritoneal, pericardial, and pleural cavities loaded with fluid and with advanced changes in its internal organs; it may even show signs of life at birth; yet it invariably dies in a few minutes, or at most hours, thereafter. The general dropsy was compatible with an intrauterine, but not with an extrauterine existence. With the occurrence of birth the infant found itself in conditions in which its diseased organs were no longer able to conserve life: the potential mortality became real. I have already referred to the enormous amount of teratological change which might be present in the fœtus without causing its intrauterine death. It is thus possible for a monstrous embryo to be born into its neofœtal period of existence and to be carried through the whole of fœtal life without interruption. The monstrosity is produced in the embryonic epoch; but the wrong lines of development then laid down continue to be followed in the fœtal period, and the process is only brought to a conclusion by death, when the organism is projected into a non-placental environment. In this manner the placenta, by preventing intrauterine death, no doubt often saves the mother from the risks of premature confinement; but for this effect the prolongation of the life of a diseased or monstrous fœtus would seem to be an unmixed evil (44).
The placental factor in fœtal pathology may be looked at from a second standpoint: the placenta may be regarded as a protection to the fœtus, as a barrier preventing sometimes, if not always, the passage of poisons and toxines from a diseased maternal organism to the fœtus. Porak (Arch. de méd, expér. et d'anat. path., vi. 192, 1894) and others have experimentally demonstrated some of the ways in which the placenta acts with regard to poisons in the maternal circulation. It has been shown that it has a real affinity for some toxic substances; and in it accumulate copper and mercury, but not lead. In addition to its pulmonary, renal, and intestinal functions, the placenta fixes glycogen and acts as an accumulator of poisons, and so resembles in its action the liver in the adult. This has been referred to in the preceding chapter. But the storing up of poisons in the placenta is not so general as the accumulation of them in the liver of the mother. While the placenta stores up poisons, it does not on that account altogether prevent their passage into the fœtal tissues; it does not act as a complete barrier. It offers, however, a varying degree of obstruction to their passage; it allows copper and lead to pass easily, arsenic with greater difficulty, and mercury apparently not at all, for Porak always found it in the placenta and never in the fœtal organs. These observations, it must be remembered, were made on guinea-pigs, and do not of necessity apply to the human subject; but in the absence of other evidence they have a considerable value.
With regard to the action of the placenta as an accumulator of pathogenic microbes and their toxines, and as a barrier to their passage to the fœtus, a great deal has been learned during the last, fifteen or twenty years; but the problems which yet remain for solution are very numerous and the difficulties associated with them
