84. If we take a placenta which has been expelled from the womb, in all its integrity, between the fifth and seventh month, when the vascularity of the decidua is considerable, and after carefully washing its surface in tepid water, we plunge it in a weak solution of alcohol, so as to harden the decidua in some degree, we shall be able to slice off the latter from the surface of the placenta, at the depth of about the tenth of an inch, without injuring the delicate texture of the membrane. This should then be carefully macerated by turning the under surface upwards, under water, when, after a time, much of the tomentous attachment seen floating, will gradually be detached, and leave part of a smooth surface behind. If the membrane be then viewed with a strong magnifying glass, on its upper surface several orifices, with regular edges, but of various aperture, will be observed, through which, if we introduce a slender pipe and blow air into them, not only the longitudinal vessels in the decidua will be seen to fill with that fluid; but the short fragments of their ramifications pendent from the under surface of the membrane, will be distended, and the air will pass through them bubbling up through the water, thus denouncing their own vascular nature and arrangement. This is _an experimentum crucis_. (Original, 1826–27). 85. The orifices in the decidua have been denied by one or two recent writers, particularly by Professor Lauth; but they are admitted by all the rest of the modern physiologists and anatomists, from Dr. Hunter down to the latest experimentalist on the subject. It is through these that the injection, thrown into the uterine vessels, while the placenta is still adhering to the uterus, passes into that part of the placental mass which is formed by the decidual ramifications. In a very beautiful and most accurately conducted experiment made at the Middlesex hospital, by Dr. H. Ley, (March, 1833,) the particulars of which, I hope, to see published by that able physician; a red injection was pushed, without any difficulty,—laceration,—or extravasation, towards the adherent placenta, from the uterine vessels of a pregnant woman, who died of a disease of the heart, undelivered; when it was found to have penetrated, in the most regular and uniform manner, to the very remotest terminal ramifications of the decidual vessels. The placenta was then carefully detached, the decidual surface was carefully examined with magnifying glasses, no laceration could be detected, except what had been made by accident or violence in a small part of its circumference while the placenta was being detached from the womb. Orifices, as distinct and as properly organized as orifices can be in membranous textures, were seen in many parts of it by more than one competent and unbiassed person; and air was blown through some of them, or a small silver pipe introduced, without effort or laceration. Not the slightest vestige of